Drug testing false-positive results

Drug/Lab test interactions False-positive results may occur in screening tests for pheochromocytoma in patients who are being treated with prazosin. 

Drug/Lab test interactions Decreased thrombocyte values may be obtained. Colchicine may cause false-positive results when testing urine for RBC or... 

Drug/Lab test interactlons Su tor am 6es may produce false-positive urinary glucose tests when performed by Benedict s method. Sulfisoxazole may interfere with the Urobilistix test and may produce false-positive results with sulfosalicylic acid tests for urinary protein. 

Olympic athletes are tested to see that they are not using illegal performance-enhancing drugs. Suppose that urine samples are taken and analyzed and the rate of false positive results is 1%. Sup-... 

We have developed special procedures for the avoidance of false positive results and for the accurate interpretation of positive results in terms of drug use, passive exposure to drugs or specimen contamination. This experience with workplace testing will be described along with an assessment of the efficacy and reliability of hair analysis. 

Types of False Positive Results in Drug Testing... 

Simple patch skin testing is naturally most useful in diagnosing contact dermatitis, but it is unreliable for other allergies. Skin prick tests are helpful in specialist hands for diagnosing IgE-dependent drug reactions, notably due to penicillin, cephalosporins, muscle relaxants, thiopental, streptokinase, cis-platin, insulin and latex. They can cause anaphylactic shock. False positive results occur. 

Antihypertensive drugs may alter catecholamine concentrations (particularly those that induce a reflex increase in sympathetic activity, e.g. vasodilators). False-positive results in tests can then occur and in the past patients have undergone unnecessary operations. ... 

When detailed qualitative and precise quantitative analyses for drugs are required, we must choose instrument-based testing without immunoreactions, because the latter cannot discriminate the parent drugs from its metabolites/derivatives and chemicals that have similar structures. For example, putrefactive amines, such as phenethylamine, frequently give false positive results for amphetamines dihydrocodeine gives positive results for opiates. However, immunoassay kits for chemical compounds are still useful, especially in screening. 

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