Articles on Medical Diseases and Conditions

Tag: Biliary Tract Tests

  • Blood Ammonia

    One function of the liver is the synthesis of urea from various sources of ammonia, most of which come from protein-splitting bacteria in the GI tract. In cirrhosis, there is extensive liver cell destruction and fibrous tissue replacement of areas between nodules of irregularly regenerating liver cells. This architectural distortion also distorts the hepatic venous blood supply and leads to shunting into the systemic venous system, a phenomenon often manifested by esophageal varices. Thus, two conditions should exist for normal liver breakdown of ammonia: (1) enough functioning liver cells must be present and (2) enough ammonia must reach these liver cells. With normal hepatic blood flow, blood ammonia elevation occurs only in severe liver failure. With altered blood flow in cirrhosis, less severe decompensation is needed to produce elevated blood ammonia levels. Nevertheless, the blood ammonia is not directly dependent on the severity of cirrhosis but only on the presence of hepatic failure.

    Hepatic failure produces a syndrome known as “prehepatic coma” (hepatic encephalopathy), which progresses to actual hepatic coma. Clinical symptoms of prehepatic coma include mental disturbances of various types, characteristic changes on the electroencephalogram, and a peculiar flapping intention tremor of the distal extremities. However, each element of this triad may be produced by other causes, and one or more may be lacking in some patients. The ensuing hepatic coma may also be simulated by the hyponatremia or hypokalemia that cirrhotic patients often manifest or by GI bleeding, among other causes. Cerebrospinal fluid glutamate levels are currently the most reliable indicator of hepatic encephalopathy. However, this requires spinal fluid, and in addition, the test is often not available except in large medical centers or reference laboratories. Of more readily available laboratory tests, the blood ammonia level shows the best correlation with hepatic encephalopathy or coma. However, the blood ammonia level is not elevated in all of these patients, so that a normal blood ammonia level does not rule out the diagnosis. Arterial ammonia levels are more reliable than venous ones since venous ammonia may increase to variable degree compared to arterial values. RBCs contain about 3 times the ammonium content of plasma, so that hemolysis may affect results. Muscular exertion can increase venous ammonia. Plasma is preferred to serum since ammonia can be generated during clotting. Patient cigarette smoking within 1 hour of venipuncture may produce significant elevation of ammonia. One investigator reported transient ammonia elevation at 0.5-3 hours and again at 3.5-6 hours after a meal containing protein in some normal persons, with the effect being magnified in persons with liver disease.

    Blood ammonia has been proposed as an aid in the differential diagnosis of massive upper GI tract bleeding, since elevated values suggest severe liver disease and thus esophageal varices as the cause of the bleeding. However, since cirrhotics may also have acute gastritis or peptic ulcer, this use of the blood ammonia level has not been widely accepted. At present, the blood ammonia is used mainly as an aid in diagnosis of hepatic encephalopathy or coma, since elevated values suggest liver failure as the cause of the symptoms. Otherwise, ammonia determination is not a useful liver function test, since elevations usually do not occur until hepatic failure.

  • Serum Bile Acids

    Bile acids are water-soluble components of bile that are derived from cholesterol metabolism by liver cells. Two primary bile acids are formed: cholic acid and chenodeoxycholic acid. Both are conjugated with glycine or taurine molecules and excreted from liver cells into bile in a manner similar but not identical to bilirubin excretion. The conjugated bile acids are stored in the gallbladder with bile and released into the duodenum, where they help to absorb fat and fat-soluble material. About 95% of the bile acids are reabsorbed from the jejunum and ileum and taken through the portal vein back to the liver, where they are reextracted by liver cells and put back into the bile. Cholic acid is reabsorbed only in the terminal ileum. A small proportion of circulating bile acids is excreted by the kidneys and a small proportion reaches the colon, where is undergoes some additional changes before being reabsorbed and taken back to the liver.

    At least two cycles of bile acid metabolism occur in the 2 hours following a meal. Normally, 2-hour postprandial bile acid levels are increased 2-3 times fasting levels. Even so, the values are relatively low.

    Due to the metabolic pathways of bile acids, diseases affecting hepatic blood flow, liver cell function (bile acid synthesis), bile duct patency, gallbladder function, and intestinal reabsorption can all affect serum bile acid levels. However, intestinal malabsorption is uncommon and usually does not simulate liver disease. Although gallbladder disease (cholecystitis or cholelithiasis) can occasionally mimic liver disease and may be associated with common bile duct obstruction, most cases of primary gallbladder disease can be differentiated from primary liver disease. Therefore, bile acid abnormality is relatively specific for liver or biliary tract disease. Both cholic acid and chenodeoxycholic acid can be measured by immunoassay techniques. Cholic acid assay is more readily available at the present time. The assays are not widely available but can be obtained in university centers or large reference laboratories. Because values fluctuate during the day and are affected by food, specimens should be obtained at the same time of day (usually in the early morning) and the same relationship to meals.

    Bile acid assay is said to be the most sensitive test available to detect liver or biliary tract dysfunction. The 2-hour postprandial level is more sensitive than the fasting level, which itself is more sensitive than any one of the standard liver function tests. In most reports serum bile acid, even using a fasting specimen, was 10%-20% more sensitive than any other single liver function test in various types of liver and biliary tract conditions. There are only a few investigators who report otherwise. Bile acids are frequently abnormal in inactive cirrhosis when all other biochemical liver tests are normal and are frequently abnormal in resolving hepatitis when other tests have subsided below the upper limits of their reference ranges. Bile acid assay has mostly replaced bromsulphalein (BSP) and indocyanine green (CardioGreen) for this purpose. A normal bile acid assay, especially the 2-hour postprandial value, is excellent evidence against the presence of significant liver or biliary tract disease. There have not been sufficient studies to establish the exact sensitivity of bile acid assay in early metastatic tumor to the liver. The major advantages of bile acid assay, therefore, are its sensitivity in most types of liver and biliary tract disease and its relative specificity for the liver and biliary tract. One report indicates that bile acids may be elevated by phenytoin or isoniazid therapy.

    Bile acid assay might also be useful to prove liver origin of abnormal liver function test results in those cases where tests like GGT are equivocal or are affected by nonhepatic conditions that could produce falsely elevated values. Bile acid assay could theoretically be used to differentiate jaundice due to hemolysis from that due to liver disease but is rarely necessary for this purpose. Bile acid assay has been suggested as a test for intestinal malabsorption, but few reports are available on this subject.

    The major drawback of bile acid assay is lack of ability to differentiate among the various types of liver or biliary tract disease. Bile acid assay cannot differentiate between intrahepatic and extrahepatic biliary tract obstruction. Nearly anything that produces liver or biliary tract abnormality can affect the bile acid values. Although some conditions produce statistically different degrees of abnormality than other conditions, there is too much overlap when applied to individual patients for the test to be of much help in differential diagnosis. However, there are a few exceptions. Bile acid assay may be useful in the differential diagnosis of congenital defects in bilirubin metabolism (e.g., Gilbert’s syndrome and Dubin-Johnson syndrome;. In neonatal biliary obstruction, there are some reports that oral administration of cholestryamine, an anion exchange resin that binds the bile acids, can aid in differentiating neonatal hepatitis with patent common bile duct from common duct atresia by lowering serum bile acid values if the duct is patent.

    In summary, bile acid assay is useful (1) to screen for liver disease when other liver function tests are normal or give equivocal results; (2) in some cases, to help differentiate between hepatic and nonhepatic causes of other liver test abnormalities; (3) in some cases, to follow patients with liver disease when other tests have returned to normal; and (4) to help differentiate certain congenital diseases of bilirubin metabolism.

  • Prothrombin Time (PT)

    In certain situations the prothrombin time can be a useful liver test. The liver synthesizes prothrombin but needs vitamin K to do so. Vitamin K is a fat-soluble vitamin that is present in most adequate diets and is also synthesized by intestinal bacteria; in either case, it is absorbed from the small bowel in combination with dietary fat molecules. Consequently, interference with vitamin K metabolism can take place because of (1) lack of vitamin K due to dietary deficiency, destruction of intestinal bacteria, or defective intestinal absorption due to lack of bile salts or through primary small bowel malabsorption; (2) inadequate utilization secondary to destruction of liver parenchyma; or (3) drugs, due to coumarin anticoagulants or certain cephalosporin antibiotics. Normally, the body has considerable tissue stores of vitamin K, so that it usually takes several weeks to get significant prothrombin deficiency on the basis of inadequate vitamin K alone. However, as noted in the discussion of PT in Chapter 8, low vitamin K intake because of anorexia or prolonged IV feeding can be potentiated by antibiotics, other medications, or poor absorption. Nevertheless, the usual cause of prothrombin abnormality is liver disease. In most cases it takes very severe liver disease, more often chronic but sometimes acute, before prothrombin levels become significantly abnormal. In the usual case of viral hepatitis, the PT is either normal or only slightly increased. In massive acute hepatocellular necrosis the PT may be significantly elevated, but it seems to take a few days to occur. In mild or moderate degrees of cirrhosis the PT is usually normal. In severe end-stage cirrhosis the PT is often elevated. The test most often used to differentiate PT elevation due to liver cell damage from other conditions that affect vitamin K supply or metabolism is to administer an intravenous or intramuscular dose of vitamin K and then repeat the PT 24-48 hours later. PT elevation due to liver cell damage usually does not respond to parenteral vitamin K therapy, whereas the PT will return to reference range in other conditions affecting vitamin K. In metastatic carcinoma the PT is usually normal unless biliary tract obstruction is present.

    Some Etiologies for Gamma-Glutamyltransferase (GGT) Elevation
    Liver space-occupying lesions (M-H)* (88%, 45%-100%)†
    Alcoholic active liver disease (M, occ H) (85%, 63%-100%)
    Common bile duct obstruction (M-H) (90%, 62%-100%)
    Intrahepatic cholestatis (M-H) (90%, 83%-94%)
    Biliary tract acute inflammation (M-H) (95%, 90%-100%)
    Acute hepatitis virus hepatitis (M, occ H) (95%, 89%-100%)
    Infectious mononucleosis (M/S, occ H) (90%)
    Cytomegalovirus acute infection (S/M) (75%)
    Acute pancreatitis (M, occ H) (85%, 71%-100%)
    Active granulation tissue formation (S-M)
    Acetaminophen overdose (S/M)
    Dilantin therapy (S, occ M) (70%, 58%-90%)
    Phenobarbitol (similar to Dilantin)
    Severe liver passive congestion (S) (60%)
    Reye’s syndrome (S) (63%)
    Other; all usually S elevations
    Acute MI (5%-30%)
    Tegretol (30%)
    Hyperthyroidism (0%-62%)
    Epilepsy (50%-85%)
    Brain tumor (57%)
    Diabetes mellitus (24%-57%)
    Non-alcohol fatty liver
    *S, Small (1-3X upper limit); M, Moderate (3-5X); H, High (over 5X)
    †Percentage of patients, with literature range

    Certain conditions not involving liver disease or vitamin K absorption can affect the PT. Anticoagulant therapy with coumarin drugs or heparin is discussed in Chapter 8. Heparin flushes, blood with a very high hematocrit level, and severe hyperlipemia (when photo-optical readout devices are used) can produce artifactually elevated PT results. Various medications can affect the PT.

  • Gamma-Glutamyltransferase (GGT)

    GGT (formerly gamma-glutamyltranspeptidase) is located mainly in liver cells, to a lesser extent in kidney, and in much smaller quantities in biliary tract epithelium, intestine, heart, brain, pancreas, and spleen. Some GGT activity seems to reside in capillary endothelial cells. The serum GGT level is increased in the newborn but declines to adult levels by age 4 months. One report found that obese persons could have GGT values up to 50% higher than nonobese persons. By far the most common cause of serum GGT elevation is active liver disease. GGT is affected by both acute liver cell damage and biliary tract obstruction. In biliary tract obstruction and space-occupying lesions of the liver, GGT was found by some investigators to have the same sensitivity as ALP (with a few cases of metastatic tumor to liver abnormal by GGT but not by ALP and vice versa) and is reported to be more sensitive than ALP by other investigators. Overall sensitivity for metastatic liver tumor is said to be about 88% (literature range, 45%-100%) compared to about 80% for ALP. In acute liver cell injury, GGT levels are elevated with approximately the same frequency as the AST. Therefore, GGT has overall better sensitivity than either ALP or AST in liver disease. GGT levels are elevated in about 90% of patients with infectious mononucleosis (Epstein-Barr virus) and about 75% with cytomegalovirus infection, presumably due to liver involvement from these viruses.

    GGT levels are not significantly affected by “normal” alcoholic beverage intake in most cases. In heavy drinkers and chronic alcoholics, GGT levels are reported to be elevated in about 70%-75% of patients (literature range, 63%-80%). Determining the GGT level has been advocated as a screening procedure for alcoholism.

    GGT levels may become elevated in several conditions other than liver disease (see the box).

    About 5%-30% of patients with acute myocardial infarction develop elevated GGT levels. This is usually attributed to proliferation of capillaries and fibroblasts in granulation tissue. The increase is usually reported 7-14 days after infarction. However, a few investigators found the elevation soon after infarction, and it is unclear how many cases are actually due to liver passive congestion rather than infarct healing. The GGT level may be transiently increased by extensive reparative processes anywhere in the body.

    GGT levels are usually not increased in bone disease, childhood or adolescence, and pregnancy, three nonhepatic conditions that are associated with increased ALP levels. GGT has therefore been used to help differentiate liver from nonliver origin when ALP levels are increased. However, the possible nonhepatic sources for GGT must be kept in mind.

  • Lactic Dehydrogenase (LDH)

    Lactic dehydrogenase (LDH) is found in heart, skeletal muscle, and RBCs, with lesser quantities in lung, lymphoid tissue, liver, and kidney. A considerable number of conditions can elevate total LDH levels. For that reason, serum total LDH has not been very helpful as a liver function test. However, in some cases isoenzyme fractionation by electrophoresis of elevated total LDH can help indicate the origin of the elevation and therefore help interpret the total liver function test pattern. For unknown reasons, LDH is a relatively insensitive marker of hepatic cell injury, with values usually remaining less than 3 times the upper reference limit even in acute hepatitis virus hepatitis. However, occasional patients with hepatitis virus hepatitis, infectious mononucleosis, and severe liver damage from other causes may have values greater than 3 times the upper limits. Metastatic liver tumor sometimes is associated with very high LDH values, presumable due to the widespread tumor.

    LDH can be fractionated into five isoenzymes using various methods. The electrophoretically slowest moving fraction (fraction 5) is found predominantly in liver and skeletal muscle. Compared to total LDH, the LDH-5 fraction is considerably more sensitive to acute hepatocellular damage, roughly as sensitive as the AST level, and is more specific. Degree of elevation is generally less than that of AST.

  • Serum Alanine Aminotransferase (ALT)

    ALT is an enzyme found predominantly in liver but with a moderate-sized component in kidney and small quantities in heart and skeletal muscle. In general, most ALT elevations are due to liver disease, although large amounts of tissue damage in the other organs mentioned may also affect serum levels. In fact, severe myositis or rhabdomyolysis can sometimes raise ALT to levels ordinarily associated with acute hepatitis virus hepatitis. ALT levels are elevated to approximately the same degree and frequency as AST in hepatitis virus hepatitis, infectious mononucleosis, and drug-induced acute liver cell injury. ALT levels are elevated less frequently than AST and usually to a lesser degree in acute alcoholic liver disease or active cirrhosis, liver passive congestion, long-standing extrahepatic bile duct obstruction, and metastatic tumor to the liver. ALT has been used predominantly to help confirm liver origin of an AST increase (although there are some limitations in ALT specificity) and occasionally as an aid in the differential diagnosis of liver disease by means of the AST/ALT ratio.

    One report found that the normal ALT mean value was about 1.5 times higher in African-American males and 1.8 times higher in Hispanic males than in European males. The same study found that European male mean values were 40% higher than those of European females, African-American females were 20% higher, and Hispanic females, 40% higher.

  • Serum Aspartate Aminotransferase (AST)

    Serum aspartate aminotransferase (AST; formerly SGOT) is an enzyme found in several organs and tissues, including liver, heart, skeletal muscle, and RBCs. AST elevation from nonhepatic sources is discussed elsewhere.

    AST elevation originating from the liver is due to some degree of acute liver cell injury. Following onset of acute hepatocellular damage from any etiology, AST is released from damaged cells. The serum level becomes elevated in approximately 8 hours, reaches a peak in 24-36 hours, and returns to normal in 3-6 days if the episode is short lived. In mild injury, serum levels may be only transiently and minimally elevated or may even remain within reference limits. In acute hepatitis virus, AST levels frequently become elevated more than 10 times the upper reference range limit (about 75% of patients in one study and 100% in another) and typically rise more than 20 times the upper limit (about 45% of patients in the first study and 90% in the second). In fact, a serum AST more than 20 times normal usually includes acute hepatitis virus infection in the differential diagnosis. However, 1-2 weeks later the values fall toward normal, so that a test sample drawn in the subsiding phase may show moderate or possibly only mild abnormality. In extrahepatic obstruction there usually is no elevation unless secondary parenchymal acute damage is present; when elevations occur, they are usually only mild to moderate (<10 times the upper reference limit). However, when extrahepatic obstruction occurs acutely, AST values may quickly rise to values more than 10 times normal, then fall swiftly after about 72 hours. In cirrhosis, whether the AST level is abnormal and (if abnormal) the degree of abnormality seems to depend on the degree of active hepatic cell injury taking place. Inactive cirrhosis usually is associated with normal AST levels. In active alcoholic cirrhosis, AST elevation is most often mild to moderate, with the majority of AST values less than 5 times the upper range limit and over 95% of AST values less than 10 times normal. In active chronic hepatitis virus hepatitis, AST values are also usually less than 10 times normal. However, one group reported that about 15% of their patients had at some time values more than 10 times normal. However, some of these patients could have superimposed acute infection by non-A, non-B or delta hepatitis virus. In liver passive congestion, AST levels are elevated in 5%-33% of patients. About 80% of these patients have AST elevations less than 3 times normal. In severe acute congestive failure, liver hypoxia may be severe, and one study estimated that about 50% of these patients have AST elevation. In some of these patients AST levels may be higher than 3 times normal and occasionally may even exceed 20 times normal (about 1% of patients with substantial degrees of congestive failure). In some cases AST elevation due to acute myocardial infarction adds to AST arising from the liver. In infectious mononucleosis, AST levels are elevated in 88%-95% of patients, but only about 5% of elevations are greater than 10 times normal and about 2% are more than 20 times normal.

    Some Etiologies for Aspartate Aminotransferase Elevation
    Heart
    Acute myocardial infarct
    Pericarditis (active: some cases)
    Liver
    Hepatitis virus, Epstein-Barr, or cytomegalovirus infection
    Active cirrhosis
    Liver passive congestion or hypoxia
    Alcohol or drug-induced liver dysfunction
    Space-occupying lesions (active)
    Fatty liver (severe)
    Extrahepatic biliary obstruction (early)
    Drug-induced
    Skeletal Muscle
    Acute skeletal muscle injury
    Muscle inflammation (infectious or noninfectious)
    Muscular dystrophy (active)
    Recent surgery
    Delirium tremens
    Kidney
    Acute injury or damage
    Renal infarct
    Other
    Intestinal infarction
    Shock
    Cholecystitis
    Acute pancreatitis
    Hypothyroidism
    Heparin therapy (60%-80% of cases)

    There is a large group of common diseases with mild or moderate AST elevation (defined arbitrarily as elevated less than 10 times the upper reference limit); these include acute hepatitis in the subsiding or recovery phases, chronic hepatitis, active cirrhosis or alcoholic liver disease, liver passive congestion, drug-induced liver dysfunction (including intravenous [IV] or subcutaneous heparin), metastatic liver tumor, long-standing extrahepatic bile duct obstruction, infectious mononucleosis, cytomegalovirus (88%-95%; 2% more than 10 times normal), and fatty liver (40%; rare > 5 x normal). As mentioned earlier, in a few patients with active cirrhosis, liver congestion, infectious mononucleosis, and drug-induced liver injury, the AST may attain levels more than 20 times upper reference limit that are suggestive of acute hepatitis virus infection. AST levels are elevated in approximately 50% of patients with liver metastases, with most elevations less than 5 times the upper reference limit. One report found that obese patients had upper reference limits up to 50% higher than normal-weight persons.

    In active alcoholic cirrhosis, liver congestion, and metastatic tumor to the liver, the AST level usually is considerably higher than the alanine aminotransferase (ALT; formerly SGPT) level, with an AST/ALT ratio greater than 1.0. Ratios less than 1.0 (ALT equal to or greater than AST) are the typical finding in acute hepatitis virus hepatitis and infectious mononucleosis. However, about 30% of patients with acute hepatitis virus infection and some patients with infectious mononucleosis have a ratio greater than 1.0; and ratios either greater than or less than 1.0 may occur in patients with AST elevation due to extrahepatic obstruction. The ratio tends to be more variable and less helpful when the AST value is greater than 10 times the upper reference limit. Some prefer to use an AST/ALT ratio of 1.5 or 2.0 rather than 1.0 as the cutoff point (i.e., an AST value more than twice the ALT value is more suggestive of alcoholic active cirrhosis than hepatitis virus hepatitis, especially if the AST value is less than 10 times normal). Although most agree that active alcoholic liver disease usually yields AST values significantly higher than ALT, there is disagreement in the literature on the usefulness of the ratio (especially the 1.0 value) for diagnosis of individual patients.

  • Alkaline Phosphatase (ALP)

    Alkaline phosphatase (ALP) is a group of closely related enzymes with maximal activity when the pH is about 10. ALP is found in many tissues, with highest concentrations in liver and biliary tract epithelium, bone, intestinal mucosa, and placenta. Liver and bone are the two tissues most commonly responsible for ALP elevation. ALP is composed of several isoenzymes, and each of the major sources of ALP contains a different isoenzyme. Reference range values are about 1.5-2.0 times higher in children than in adults due to active bone growth. Even higher levels occur during the adolescent “growth spurt,” which occurs in girls aged 8-12 years and boys aged 10-14 years. Peak reference values for adolescents are reported to be 3-5 times adult values, although occasional persons are said to have values as high as seven times the adult upper reference range. Three times the adult reference range is more typical in my experience. Adult values were reported in girls by age 16 and in boys at approximately age 20.

    Alkaline phosphatase of liver origin

    In liver, ALP is formed by liver cells and biliary tract mucosal cells. It is excreted into bile through a different mechanism from that controlling bilirubin excretion. Although ALP of liver origin can be increased in serum during any type of active liver disease, the serum level is especially sensitive to biliary tract obstruction, whether intrahepatic or extrahepatic, whether mild or severe, or whether localized in a small area of the liver or more extensive. As a general rule, the degree of ALP elevation reflects the severity of obstruction and the amount of biliary tissue involved. Unfortunately, there is considerable variation in behavior of ALP among individual patients.

    Common etiologies for ALP elevation are listed in the box. The three liver conditions most frequently associated with ALP elevation are extrahepatic (common bile duct) biliary tract obstruction, intrahepatic biliary tract obstruction due to acute liver cell injury, and liver space-occupying lesions (tumor, abscess, granulomas). Common bile duct obstruction, metastatic tumor to the liver, and the uncommon condition of primary biliary cirrhosis are the most frequent etiologies for persistent ALP elevation more than 3 times the upper reference limit. However, metastatic tumor may be present with lesser degrees of elevation or with no elevation. On the other hand, acute liver cell injury occasionally may produce ALP elevation more than 3 times the upper reference limit. In one or more reports, ALP elevation 5 times the upper reference limit or more occurred in 5% of patients with hepatitis virus hepatitis, 13%-20% of those with infectious mononucleosis, and 5% of persons with active alcoholic cirrhosis. Drug-induced liver dysfunction is another consideration.

    Most Common Causes for Alkaline Phosphatase Elevation

    Liver and biliary tract origin
    Extrahepatic bile duct obstruction
    Intrahepatic biliary obstruction
    Liver cell acute injury
    Liver passive congestion
    Drug-induced liver cell dysfunction
    Space-occupying lesions
    Primary biliary cirrhosis
    Sepsis
    Bone origin (osteoblast hyperactivity)
    Physiologic (rapid) bone growth (childhood and adolescent)
    Metastatic tumor with osteoblastic reaction
    Fracture healing
    Paget’s disease of bone
    Capillary endothelial origin
    Granulation tissue formation (active)
    Placental origin
    Pregnancy
    Some parenteral albumin preparations
    Other
    Thyrotoxicosis
    Benign transient hyperphosphatasemia
    Primary hyperparathyroidism

    In metastatic carcinoma to the liver, ALP levels are elevated in about 75%-80% of cases (literature range, 42%-100%). ALP levels are also elevated in hepatoma, liver abscess, liver granulomas, and other active liver space-occupying lesions. The frequency of ALP elevation is not as well documented in these conditions as in metastatic tumor but apparently is similar. In extrahepatic biliary tract (common bile duct) obstruction or in primary biliary cirrhosis, ALP levels are elevated in nearly 100% of patients except in some cases of incomplete or intermittent obstruction. Values are usually greater than three times the upper reference range limit, and in the most typical cases exceed 5 times the upper limit. Elevation less than 3 times the upper limit is some evidence against complete extrahepatic obstruction. In patients with jaundice due to intrahepatic obstruction (most often severe active cirrhosis or hepatitis virus hepatitis), ALP levels are usually elevated and can exhibit a wide range of values. Most often the levels are less than 3 times the upper reference limit, but 5%-10% of patients have a greater degree of elevation. In nonjaundiced patients with active liver cell damage, ALP levels are elevated in about one half of the cases, usually less than 3 times the upper reference limit. Inactive cirrhosis or uncomplicated mild fatty liver usually does not result in ALP elevation. Fifteen percent to 20% of patients with infectious mononucleosis have ALP values greater than 3 times normal, even though liver biopsy shows relatively mild liver changes. Alkaline phosphatase levels are elevated in about 10%-20% of patients with liver passive congestion, with values usually less than twice normal. It may be higher in a few patients.

    Alkaline phosphatase of bone origin

    Sources other than the liver can elevate serum ALP levels either alone or concurrently with liver source ALP elevation. Bone is by far the most frequent extrahepatic source. Osteoblasts in bone produce large amounts of ALP, and greatly increased osteoblastic activity hinders usefulness of ALP determination as a liver function test. Normal bone growth of childhood and adolescence, healing fractures, Paget’s disease of bone (85% of cases in early stage; 100% later), hyperparathyroidism, rickets and osteomalacia, and osteoblastic metastatic carcinoma to bone all consistently produce elevated values. In a patient with jaundice, however, one can surmise that at least a portion of an ALP elevation is due to liver disease.

    When doubt exists as to the origin of the increased ALP values, several alternatives are available. One possibility is use of another enzyme that provides similar information to ALP in liver disease but is more specific for liver origin. Enzymes that have been widely used for this purpose are 5′-nucleotidase (5-NT) and gamma-glutamyltransferase (GGT). Of these, the methodology of 5-NT is probably a little too difficult for reliable results in the average laboratory; also, according to at least one report, about 10% of patients with bone disease may display slight elevation. The GGT has sensitivity equal to or greater than ALP in obstructive liver disease and greater sensitivity in hepatocellular damage. Various reports in the literature state that the GGT level is not elevated in bone disease. However, some data in these reports suggest that GGT may occasionally be mildly elevated in bone disease. Another method for differentiating tissue origin of ALP is isoenzyme separation of specific ALP bone and liver fractions by the use of heat, chemical, enzymatic, or electrophoretic techniques. Of these, electrophoresis is the most difficult but probably the most reliable and informative.

    Other sources of alkaline phosphatase elevation

    In pregnancy, the placenta produces ALP; ALP of placental origin begins to rise at about the end of the first trimester and can reach values up to 4 times the upper reference limit in the third trimester. However, the pregnancy-related increase in ALP also has a bone-derived component, with placental ALP comprising about 60% of total serum ALP in the second and third trimesters. Placental ALP has a half-life of about 7 days and in most patients is gone by 3-6 days after delivery. Bone-derived ALP is longer-lived and can persist even more than 6 weeks after delivery. However, only a very few patients have an elevated ALP level from pregnancy alone that persists more than 4 weeks postpartum. In 100 consecutive patients in our hospital at time of delivery, 15% had an ALP level within reference range, 50% had elevated ALP between 1-2 times the upper normal limit, 29% had values between 2-3 times the upper limit, and 6% had values between 3-4 times the upper limit.

    Certain persons whose blood belongs to group B or O and secrete ABH substance are reported to show an increase of ALP (of intestinal isoenzyme origin) about 2 hours after a fatty meal. ALP levels may become elevated following therapeutic administration of albumin, since some companies use placental tissue as the source for their albumin. ALP levels can become elevated 7-14 days after severe tissue damage or infarction due to ALP produced by fibroblasts and endothelial cells proliferating in new granulation tissue. ALP levels are reported elevated in 42%-89% of patients with hyperthyroidism. In one report, about half had elevation in both the bone and liver isoenzyme. The remainder had elevation either of bone or liver fraction. The bone fraction usually increases after therapy of hyperthyroidism and can remain elevated for a long time. Certain medications that may affect the liver (see Table 37-2; XIV) may sometimes be associated with ALP elevation. The most frequent of these is phenytoin (Dilantin). ALP levels are elevated in about 40%-50% (range, 22%-63%) of patients taking phenytoin, with values in most cases not exceeding twice the upper reference limit. Elevation of ALP has been reported in a few patients with sepsis.

    Benign transient hyperphosphatasemia usually occurs in young children, but can occur in older children and rarely even in adults. Patients are reported to have a variety of illnesses, including infection, but no one condition heavily predominates as a possible cause. The ALP level is usually more than 5 times the upper adult limit (which calls attention to the patient) and frequently is considerably higher than that. The ALP level usually returns to reference range in 2-4 months but occasionally elevation persists longer. Various ALP isoenzyme patterns have been reported, including bone only, liver only, and more commonly, bone plus liver or bone plus liver plus a third isoenzyme migrating next to liver between bone and liver.

  • Urine Bilirubin and Urobilinogen

    These tests follow much the same pattern as conjugated and unconjugated bilirubin. After bile reaches the duodenum, intestinal bacteria convert most of the bilirubin to urobilinogen. Much urobilinogen is lost in the feces, but part is absorbed into the bloodstream. Once in the blood, most of the urobilinogen goes through the liver and is extracted by hepatic cells. Then it is excreted in the bile and once again reaches the duodenum. Not all the blood-borne urobilinogen reaches the liver; some is removed by the kidneys and excreted in urine. Normally, there is less than 1 Ehrlich unit, or no positive result at greater than a 1:20 urine dilution.

    Conjugated bilirubin, like urobilinogen, is partially excreted by the kidney if the serum level is elevated. Unconjugated bilirubin cannot pass the glomerular filter, so it does not appear in urine. However, when the serum unconjugated bilirubin level is high, more conjugated bilirubin is produced and excreted into the bile ducts; consequently, more urobilinogen is produced in the intestine. Additional urobilinogen is reabsorbed into the bloodstream and a portion of this appears in the urine, so that increased urine urobilinogen is found when increased unconjugated bilirubin is present. When increased serum unconjugated bilirubin is due only to increased RBC destruction, the serum conjugated bilirubin level is close to normal, because the liver excretes most of the conjugated bilirubin it produces into the bile ducts. Since the serum conjugated bilirubin level is normal in jaundice due to hemolytic anemia, the urine does not contain increased conjugated bilirubin.

    When complete biliary obstruction occurs, no bile can reach the duodenum and no urobilinogen can be formed. The stool normally gets its color from bilirubin breakdown pigments, so that in complete obstruction the stools lose their color and become gray-white (so-called clay color). The conjugated bilirubin in the obstructed bile duct backs up into the liver, and some of it escapes (regurgitates) into the bloodstream. Serum conjugated bilirubin levels increase, and when these levels are sufficiently high, tests for urine conjugated bilirubin give positive results. In cases of severe hepatocellular damage, urobilinogen is formed by the intestine and absorbed into the bloodstream as usual. The damaged liver cells cannot extract it adequately, however, and thus increased amounts are excreted in urine. In addition, there may be conjugated bilirubin in the urine secondary to leakage into the blood from damaged liver cells. Incidentally, urine bilirubin is often called bile, which is technically incorrect, since conjugated bilirubin is only one component of bile. However, custom and convenience make the term widely used.

    In summary, there is an increased urine conjugated bilirubin level when the serum conjugated bilirubin level is elevated but usually not until the serum conjugated bilirubin exceeds the reference range upper limit for total serum bilirubin. It is rarely necessary to order urine bilirubin determinations, since the serum bilirubin level provides more information. Increased urine urobilinogen may occur due to increased breakdown of blood RBCs or due to severe liver cell damage. Urine urobilinogen determination rarely adds useful information to other tests in conditions that produce increased urobilinogen excretion. In addition, there is the problem of inaccuracy due to urine concentration or dilution.

  • Serum Bilirubin

    Bilirubin is formed from breakdown of hemoglobin molecules by the reticuloendothelial system. Newly formed (unconjugated) bilirubin circulates in blood bound nonpermanently to serum albumin and is carried to the liver, where it is extracted by hepatic parenchymal cells, conjugated first with one and then with a second glucuronide molecule to form bilirubin diglucuronide, and then excreted in the bile. The bile passes through the common bile duct into the duodenal segment of the small intestine. It has been well documented that when a certain diazo compound discovered by van den Bergh is added to conjugated bilirubin, there will be color development maximal within 1 minute. This fast-reacting bilirubin fraction consists of bilirubin monoglucoronide, bilirubin diglucoronide, and a third fraction consisting of conjugated bilirubin (monoglucoronide) bound permanently and covalently to albumin, called “delta bilirubin.” If alcohol is then added, additional color development takes place for up to 30 minutes. This second component, which precipitates with alcohol, corresponds to unconjugated bilirubin. Actually color continues to develop slowly up to 15 minutes after the simple van den Bergh reaction maximal at 1 minute, and this extra fraction used to be known as the “delayed,” or “biphasic reaction.” It has since been shown that a considerable proportion of the substance involved is really unconjugated bilirubin. Since unconjugated bilirubin is measured more completely by the 30-minute alcohol precipitation technique, most laboratories do not report the biphasic reaction. The 1-minute van den Bergh color reaction is also called the “direct reaction” and the conjugated bilirubin it measures is known as “direct-acting bilirubin,” whereas the 30-minute alcohol measurement of unconjugated bilirubin is called the “indirect reaction” and its substrate is “indirect bilirubin.” Reference values are less than 1.5 mg/100 ml (25 µmol/L) for total bilirubin and less than 0.4 mg/100 ml (range, 0.2-0.5 mg/100 ml [3.42-8.55 µmol/L] depending on the method used) for 1-minute (“direct”) bilirubin.

    There are certain problems with current measurements of conjugated bilirubin that affect clinical interpretation, especially regarding neonatal bilirubin. For many years the terms “direct” and “conjugated” bilirubin were used interchangeably, and in fact, were not far from the same using standard manual methods. However, with bilirubin now being assayed predominately by automated chemistry equipment, it is becoming evident that various combinations of reagents and automated equipment vary significantly in how much unconjugated bilirubin and delta bilirubin are included in “conjugated” bilirubin assay results. Therefore, it might be more realistic to use the old terminology (direct bilirubin). For example, in one specimen from a national organization’s proficiency test program that was supposed to contain 0.3 mg/100 ml (5.13 µmol/L) of conjugated bilirubin, six different instrument/reagent combinations obtained a value of 0.26 mg/100 ml (4.4 µmol/L) or less; three other instrument/reagent combinations reported a value of 1.04-1.13 mg/100 ml (17.7-19.3 µmol/L); and seven instrument/reagent combinations returned values between 0.26 and 1.04 mg/100 ml (4.4-17.8 µmol/L). All of these laboratories obtained approximately the same value for total bilirubin. Our hospital had one of the high-result chemistry instruments. We then measured conjugated (direct) bilirubin in 65 newborn infants who had jaundice and total bilirubin levels between 10.0 and 25.5 mg/100 ml (171-436.1 µmol/L). In these clinically healthy newborns, nearly all of the total bilirubin would be expected to be unconjugated. We obtained a reference range of 0.1-0.4 mg/100 ml (1.71-6.84 µmol/L) in clinically normal adults. In the newborns, we obtained direct bilirubin values ranging from 0.5-1.6 mg/100 ml (8.55-27.4 µmol/L), with 26% of cases being between 1.1-1.6 mg/100 ml (18.8-27.4 µmol/L), approximately 3-4 times the upper normal limits. This would produce difficulty in interpreting infant bilirubin levels because conditions such as sepsis, hepatitis due to different viruses, medication effects on the liver, biliary atresia, galactosemia, congenital bilirubin conjugation defects, and alpha-1 antitrypsin deficiency traditionally elevate conjugated bilirubin values. Interestingly, these falsely elevated values had a somewhat random distribution within the otherwise stepwise increase following the increase in total bilirubin, and there appeared to be a limit to the false increase. Therefore, a considerable number of automated instruments are falsely reporting a certain unpredictable amount of unconjugated bilirubin as direct or conjugated bilirubin and are not adjusting their direct bilirubin reference range to take this into account.

    Another problem is that delta bilirubin may sometimes be included to some extent in direct bilirubin assay. Since delta bilirubin is bound tightly to serum albumin (which has a half-life of 19 days), this would cause apparent persistence of elevated serum direct bilirubin values (and therefore, comparable increase in total bilirubin) for several days after actual conjugated bilirubin levels had begun to fall.

    Conjugated bilirubin in serum is excreted in urine until the renal threshold of 29 mg/100 ml (495 µmol/L) is exceeded. Although there is no exact correlation, a general trend has been reported toward a rising serum conjugated bilirubin level as the serum creatinine level rises (if the serum creatinine changes are due to renal disease). Since conjugated bilirubin is also excreted into the intestine through the biliary duct system, the influence of renal function would only be evident if abnormal quantities of conjugated bilirubin were present in patient serum.

    Fasting, especially if prolonged, can increase total bilirubin values with normal proportions of conjugated and nonconjugated fractions. In one study, overnight fasting increased total bilirubin by an average of about 0.5 mg/100 ml (8.55 µmol/L) and 0.1-1.3 mg/100 ml (1.71-22.2 µmol/L). Poor renal function may decrease or delay excretion of conjugated bilirubin.

    Visible bile staining of tissue is called “jaundice.” Three major causes predominate: hemolysis, extrahepatic biliary tract obstruction, and intrahepatic biliary tract obstruction.

    Hemolysis causes increased breakdown of red blood cells (RBCs) and thus increased formation of unconjugated bilirubin. If hemolysis is severe enough, more unconjugated bilirubin may be present in the plasma than the liver can extract. Therefore, the level of total bilirubin will rise, with most of the rise due to the unconjugated fraction. The conjugated fraction remains normal or is only slightly elevated and rarely becomes greater than 1.2 mg/100 ml (20 µmol/L; unless a nonhemolytic problem is superimposed). Hemolysis may result from congenital hemolytic anemia (e.g., sickle cell anemia or other hemoglobinopathies), drug-induced causes, autoimmune disease, and transfusion reactions. An increased unconjugated bilirubin level may sometimes result from absorption of hemoglobin from extravascular hematomas or from pulmonary infarction. The unconjugated bilirubin level may also be increased in various other conditions mg/100 ml (20 µmol/L; unless a nonhemolytic problem is superimposed). Hemolysis may result from congenital hemolytic anemia (e.g., sickle cell anemia or other hemoglobinopathies), drug-induced causes, autoimmune disease, and transfusion reactions. An increased unconjugated bilirubin level may sometimes result from absorption of hemoglobin from extravascular hematomas or from pulmonary infarction. The unconjugated bilirubin level may also be increased in various other conditions. The reason is sometimes obscure. In most patients with most conditions producing unconjugated hyperbilirubinemia, the unconjugated fraction is usually less than 6 mg/100 ml (102.6 µmol/L) except for the rare Arias syndrome. In “pure” unconjugated hyperbilirubinemia, the unconjugated fraction is over 80% of total bilirubin. In one study of patients with unconjugated bilirubinemia, the most common associated diseases (collectively 60% of the total cases) included cholecystitis, cardiac disease (only 50% having overt congestive failure), acute or chronic infection, gastrointestinal (GI) tract disease (mostly ulcerative or inflammatory), and cancer.

    Extrahepatic biliary tract obstruction is caused by common bile duct obstruction, usually due to a stone or to carcinoma from the head of the pancreas. The height of the total serum bilirubin level depends on whether the obstruction is complete or only partial and how long the obstruction has existed. Also, in the majority of cases the bilirubin level stabilizes at less than 20 mg/100 ml even when there is complete common bile duct obstruction. Extrahepatic biliary tract obstruction initially produces an increase in conjugated bilirubin without affecting the unconjugated bilirubin, since obstruction of the common bile duct prevents excretion of already conjugated bilirubin into the duodenum. However, after several days, some of the conjugated bilirubin in the blood breaks down to unconjugated bilirubin. Eventually the ratio of conjugated to unconjugated bilirubin approaches 1:1. The amount of time necessary for this change in the composition of the serum bilirubin is quite variable, but there is some correlation with the amount of time that has elapsed since onset of obstruction. In addition, prolonged intrahepatic bile stasis (“cholestasis”) due to extrahepatic obstruction of the bile drainage system often produces some degree of secondary liver cell damage, which also helps to change the ratio of conjugated to unconjugated bilirubin.

    Unconjugated Hyperbilirubinemia
    A. Due to increased bilirubin production (if normal liver, serum unconjugated bilirubin is usually less than 4 mg/100 ml)
    1. Hemolytic anemia
    a) Acquired
    b) Congenital
    2. Resorption from extravascular sources
    a) Hematomas
    b) Pulmonary infarcts
    3. Excessive ineffective erythropoiesis
    a) Congenital (congenital dyserythropoietic anemias)
    b) Acquired (pernicious anemia, severe lead poisoning; if present, bilirubinemia is usually mild)
    B. Defective hepatic unconjugated bilirubin clearance (defective uptake or conjugation)
    1. Severe liver disease
    2. Gilbert’s syndrome
    3. Crigler-Najjar type I or II
    4. Drug-induced inhibition
    5. Portacaval shunt
    6. Congestive heart failure
    7. Hyperthyroidism (uncommon)

    Intrahepatic biliary tract obstruction is usually caused by liver cell injury. The injured cells may obstruct small biliary channels between liver cell groups. Some bilirubin may be released from damaged cells. Liver cell injury may be produced by a wide variety of etiologies, such as alcohol- or drug-induced liver injury; acute or chronic hepatitis virus hepatitis; certain other viruses such as Epstein-Barr (infectious mononucleosis) or cytomegalovirus; active cirrhosis; liver passive congestion, primary or metastatic liver tumor; severe bacterial infection; and biliary cirrhosis. When serum bilirubin is increased due to liver cell damage, both conjugated and unconjugated bilirubin fractions may increase in varying proportions. The unconjugated fraction may be increased because of inability of the damaged cells to conjugate normal amounts of unconjugated serum bilirubin. The conjugated fraction increase usually results from intrahepatic cholestasis secondary to bile sinusoid blockage by damaged hepatic cells.

    Other etiologies of jaundice. Carcinoma may increase serum bilirubin; either predominantly conjugated hyperbilirubin (if the common bile duct is obstructed) or by a variable mixture of conjugated and unconjugated bilirubin (if the tumor is intrahepatic). Intrahepatic tumor can obstruct intrahepatic bile ducts or destroy liver cells by compression from expanding tumor masses or by invasion and replacement of liver tissue. Total bilirubin is increased in about 45% of patients with liver metastases, with the incidence of hyperbilirubinemia reported to be about 70% for metastatic biliary tract and pancreatic carcinoma, about 50% for breast and lung carcinoma, about 35% for colon and gastric carcinoma, and about 10% for other tumors. In pancreatic, colon, and gastric metastatic tumor, total bilirubin may exceed 10 mg/100 ml in 10% or more patients. Drugs may produce bilirubin elevation of variable type and degree. Some drugs exert predominantly cholestatic (obstructive) effects, others induce hepatocellular injury, and still others have components of both cholestasis and hepatic cell injury. There are a large number of conditions that may produce elevated serum bilirubin levels with or without visible jaundice. Septicemia is one cause that is often not mentioned but that should not be forgotten. One report noted that in patients less than age 30 years, viral infections of the liver accounted for 80% of cases with jaundice. In the age group 30-60 years, viral infections accounted for 30%; alcoholic liver disease accounted for 30%, and gallstones or cancer accounted for about 10% each. Over age 60, cancer accounted for 45% of cases; gallstones accounted for 25%, and alcoholic liver disease and medications accounted for about 10% each.