A negative result for the presence of abused drugs in a urine specimen does not necessarily mean that no drug is present. It is also possible that the amount of drug was below the cut-off values used in the drug-testing protocol. Diluting urine is a simple way to beat an otherwise positive drug test if the original concentrations of drugs in the urine are just slightly above the cut-off values. To counteract this strategy, creatinine analysis in urine is an effective method to detect diluted urine. Neeedleman and Porvaznik considered a creatinine value of less than 10 mg/dL as suggestive of replacement of urine specimen largely by water (4). Beck et al. (5) reported that 11% of all urine specimens submitted to their laboratory for DOA testing were diluted. The SAMHSA program currently does not allow analysis of dilute urine specimens at lower screening and confirmation cut-offs. However, in Canada, the Correction Services of Canada (CSA) program incorporates the following lower drugs/metabolites screening and confirmation cut-offs for testing diluted urine specimens:
• Amphetamine—screening cut-off, 100 ng/mL; confirmation cut-off, 100 ng/mL;
• Benzoylecgonine (BE)—screening and confirmation cut-off, 15 ng/mL;
• Opiates—screening and confirmation cut-off, 120 ng/mL;
• Phencyclidine—screening and confirmation cut-off, 5 ng/mL;
• Cannabinoids—screening cut-off, 20 ng/mL; confirmation cut-off, 3 ng/mL.
Use of flushing and detoxification is frequently advertised as an effective means of passing drug tests. Cone et al. (6) evaluated the effect of excess fluid ingestion on false-negative marijuana and cocaine urine test results. These investigators studied the ability of Natural Clean Herbal Tea, goldenseal root, and hydrochlorothiazide to cause false-negative results. After 22 h of smoking marijuana cigarettes or intranasal administration of cocaine, volunteers drank 1 gal of either water, herbal tea, or hydrochlorothiazide, each in four doses over a 4-h period. It was found that within 2 h following these treatments, creatinine and specific gravity dropped to below 20 mg/dL and below 1.003, respectively. These levels were consistent with those of diluted specimens. In these experiments, marijuana and cocaine metabolite levels, as measured by enzyme-multiplied immunoassay technique (EMIT®, Dade-Behring), were also reduced significantly. It appeared that consumption of excess water was effective in diluting a urine specimen to cause false-negative results. However, consumption of herbal tea produced diluted urine faster than consumption of water alone.
In the sport scene, diuretics are used to flush out previously ingested banned substances by forced diuresis. The Medical Commission of the International Olympic Committee has banned the used of diuretics, and GC-MS is used to detect diuretics in urine. Deventer et al. (7) recently published a protocol to detect 18 common diuretics and probenecid in doping analysis using liquid chromatography and tandem mass spectrometry.
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