A critical review of the original literature has been made to identify drugs and other substances which interfere chemically with clinical laboratory test procedures. The nature and extent of such interference has been correlated with particular methods of analysis. Chemically, a drug or its metabolite may interfere with the accurate determination of the desired constituent. For example, methyldopa, used in the treatment of hypertension, will produce a false positive result for urinary catecholamines, since it reacts in the method to produce a green fluorescence similar to that produced by norepinephrine. This could lead to an erroneous diagnosis of pheochromocytoma. Radiographic contrast media, containing iodinated organic compounds, invalidate protein-bound iodine determinations because of their own high iodine content. Other TABULATIONS The information is arranged alphabetically according to test procedures. Subheadings, describing the analytical method affected, are followed by alphabetical listings of interfering substances. The latter are preceded by the notation (+) or (-) to indicate that the substance causes a false increase or false decrease, respectively, in test values. A substance reported to show no interference with the test is preceded by the notation (0). References are given to the original literature, but no claim is made for complete coverage. Some selection in choice of citations has been exercised, when multiple observations in substantial agreement have been reported. In some cases, we have augmented the material with personal observations or experiments and these have been so indicated. Interferences from bilirubin, hemoglobin, lipemic serum, color of urine, etc., cause obvious problems with various spectrophotometric or visual examinations. Chemical interferences from these sources have not been listed, unless special circumstances seemed to warrant them. Interferences from impurities in reagents or distilled water have not been included, with a few exceptions, inasmuch as these can normally be detected or corrected by inclusion of reagent blanks, standards, and recovery experiments. Drugs are listed by generic name, followed, in some cases, by the more common brand name or names. This information has been taken from Facts and Comparisonsl5, updated to 1972. This publication is very convenient for such cross-referencing. AMYLASE The following anticoagulants are reported to reduce plasma amylase activity about 20% as compared to serum or heparinized plasma. (-) Citrate16 (-) FluorideI (-) 0xalate16p17 BARBITURATES A. Screening tests on sewma OY urine depend upon the formation of mercuric salts which are soluble in chloroform. Addition of dithizone (diphenylthiocarbazone) results in a change of color from blue to orange if barbiturates are presentls. With diphenylczin. Chim. Acta, 41 (1972) 395-434 (+) Chlorpheniramine lg. Interferes only at toxic levels (over 4 mg/dl). (+) Diazepam (Valium). We have observed false positives with toxic overdoses only. (+) Diphenylhydantoin 18. Reported to g...
