Articles on Medical Diseases and Conditions

Entries for the ‘Various Factors Affecting Laboratory Test Interpretation’ Category

Laboratory Tests and the Medical Literature

One of the more interesting phenomena in medicine is the scenario under which new tests or new uses for old tests are introduced. In most cases the initial reports are highly enthusiastic. Also in most cases there is eventual follow-up by other investigators who either cannot reproduce the initial good results or who uncover substantial […]

Effects of Hospital Working Procedures

Several common hospital conditions may affect laboratory results without such alteration being recognized by the physician. These include intravenous fluids running at the time the test specimen is drawn, the effect of dehydration, the effect of heparin flushes on some tests, the effects of various medications, and in certain cases the administration of medication at […]

Effects of Medications

The effect of medications is a major problem since a patient may be taking several drugs or may be taking over-the-counter pharmaceuticals without reporting them to the physician. Medication effects may be manifest in several ways: drug-induced injury to tissues or organs (e.g., isoniazid-induced hepatitis), drug-induced alterations in organ function (e.g., increase in g-glutamyltransferase produced […]

Effects of Physiologic Variables

Physiologic differences between groups of persons may affect test results. These deviations may be attributable to normal metabolic alterations in certain circumstances. Some examples are age (e.g., an increase in alkaline phosphataselevels in children compared with adult values), sex (e.g., higher values for serum uric acid in males than in females), race (e.g., higher values […]

Problems with Laboratory Specimens

Specimen collection and preservation may create laboratory problems. Probably the most frequent offender is contamination of urine from female patients by vaginal or labial secretions. Using more than 10 squamous epithelial cells per low-power field in a centrifuged urine sediment as the index of probable contamination, my surveys have found this present in 20%-30% of […]

Normal (Reference) Ranges

The most important single influence on laboratory test interpretation is the concept of a normal range, within which test values are considered normal and outside of which they are considered abnormal. The criteria and assumptions used in differentiating normal from abnormal in a report, therefore, assume great importance. The first step usually employed to establish […]

Reproducibility and Accuracy

Reliability of laboratory tests is quite obviously affected by technical performance within the laboratory. The effect of these technical factors is reflected by test reproducibility and accuracy. Reproducibility (precision or inherent error) is a measure of how closely the laboratory can approach the same answer when the test is performed repeatedly on the same specimen. […]

Predictive Value

In recent years, Galen and Gambino have popularized the concept of predictive value, formulas based on Bayes’ theorem that help demonstrate the impact of disease prevalence on interpretation of laboratory test results (Table 1-1). Prevalence is the incidence of the disease (or the number of persons with the disease)in the population being tested. Briefly, predictive […]

Sensitivity and Specificity

Interpretation of laboratory test results is much more complicated than simply comparing the test result against a so-called normal range, labeling the test values normal or abnormal according to the normal range limits, and then fitting the result into patterns that indicate certain diseases. Certain basic considerations underlie interpretation of any test result and often […]