Rational Use of Diagnostic Tests
For example, if a
healthy patient were subjected to 20 independent tests, there would be a 64% probability of
finding at least one abnormal result.
Interfering Factors
External factors such as feeding schedule, sample processing, or medications can interfere
with test results. A high-fat meal prior to evaluation of a serum chemistry analysis will alter
values associated with lipid metabolism and cholesterol. Diuretics may affect sodium and
potassium values. Cephalosporins may cause spurious serum creatinine levels. Corticosteroids
and most all chemotherapy drugs severely decrease lymphocyte levels. Lipemia may decrease
sodium levels, depending on the testing method used. Corticosteroids may increase alkaline
phosphatase levels. If blood samples are not processed quickly after being drawn, glucose
levels will often be artificially lowered. In general, if test results do not correlate with clinical
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