Articles on Medical Diseases and Conditions

Entries for the ‘Renal Function Tests’ Category

The Problem of Hematuria

Major etiologies of hematuria and details of available tests were discussed in Chapter 12. The problem of hematuria is somewhat different from that of proteinuria. About 4% (range, 1.2%-9%) of asymptomatic men under age 40 have microhematuria of two or more RBCs per high-power field compared with about 15% (range, 13%-19%) of clinically healthy men […]

The Problem of Proteinuria

As discussed in Chapter 12, proteinuria is not itself a renal function test but almost invariably accompanies serious renal damage. Its severity does not necessarily correlate with the amount of damaged renal parenchyma or the status of any one renal function or group of systems. Its presence and degree may, in association with other findings, […]

Azotemia (Elevated Blood Urea Nitrogen Level) and Renal Failure

Many use the term “uremia” as a synonym for azotemia, although uremia is a syndrome and should be defined in clinical terms. A BUN level of approximately 100 mg/100 ml is usually considered to separate the general category of acute reversible prerenal azotemias from the more prolonged acute episodes and chronic uremias. In general, this […]

Tests of Predominantly Tubular Function

These include specific gravity, osmolality, urine excretion of electrolytes, the free water clearance test, and certain substances secreted by renal tubules. Phenolsulfonphthalein (PSP) excretion Phenolsulfonphthalein is excreted mainly by the renal tubules. In general, results give about the same clinical information as the creatinine clearance rate since glomerular and tubular dysfunction usually occur together in […]

Postrenal (Obstruction) Azotemia

1. Ureteral or urethral obstruction by strictures, stones, external compression, pelvic tumors, and so forth 2. Obstructing tumors of bladder; congenital defects in bladder or urethra 3. Prostatic obstruction (tumor or benign hypertrophy; a very common cause in elderly men) Prerenal azotemia etiologies can be divided into two main categories: (1) decreased blood volume or […]

Renal Azotemia

1. Chronic diffuse bilateral kidney disease or bilateral severe kidney damage (e.g., chronic glomerulonephritis or bilateral chronic pyelonephritis) 2. Acute tubular necrosis (glomerular or tubular injury [or both] due to hypotension or shock with renal shutdown, traumatic or nontraumatic rhabdomyolysis, transfusion or allergic reactions, certain poisons, and precipitation of uric acid or sulfa crystals in […]

Prerenal Azotemia

1. Traumatic shock (head injuries; postsurgical hypotension) 2. Hemorrhagic shock (varices, ulcer, postpartum hemorrhage, etc.) 3. Severe dehydration or electrolyte loss (severe vomiting, diarrhea, diabetic acidosis, Addison’s disease) 4. Acute cardiac decompensation (especially after extensive myocardial infarction) 5. Overwhelming infections or toxemia 6. Excess intake of proteins or extensive protein breakdown (usually other factors are […]

Tests Reflecting Severe Glomerular Damage, Tubular Damage, or Both

Blood urea nitrogen Blood urea nitrogen (BUN) is actually measured in serum rather than whole blood and can be assayed in urine. Urea can be measured biochemically or enzymatically (with the specific enzyme urease). Few substances interfere seriously with either method. Two screening methods for BUN, called Urograph and Azostix, are commercially available. Evaluations to […]

Tests Predominantly of Glomerular Function

Clearance Tests Clearance is a theoretical concept and is defined as the volume of plasma from which a measured amount of substance can be completely eliminated (cleared) into the urine per unit of time. This depends on the plasma concentration and excretory rate, which, in turn, involve the glomerular filtration rate (GFR) and renal plasma […]

Renal Function Tests

Renal function testing and liver function testing share many of the same problems. In both the kidney and the liver a multiplicity of enzyme and transport systems coexist—some related, others both spatially and physiologically quite separate. Processes going on in one section of the nephron may or may not directly affect those in other segments. […]