URINE TESTING FOR COCAINE:

Metabolite Detectable Longer Than Expected In Some Cases

"How long will it take for crack (or cocaine) to clear out of my urine?" is a question received many times a day by the staff of the Drug & Poison Information Center. It is not a straightforward question.

First, cocaine itself is metabolized too rapidly to be measured for routine screening. When urine is being screened for the presence of cocaine, it is actually benzoylecgonine, a metabolite of cocaine, that is being measured.

Second, as to how long it will take for this metabolite to be eliminated from the urine, in some cases the answer may be longer than traditionally thought. Several studies suggest that benzoylecgonine can be detected in the urine of chronic, highdose abusers for longer periods of time than originally expected. Urine screens currently required by many employers use the minimum cutoff levels set by the National Institute of Drug Abuse (NIDA) to establish a positive drug test. A urine level of 300 nanograms per milliliter (or 300 micrograms per liter) of benzoylecgonine is considered a positive result for cocaine use. However, these levels can vary in the same individual depending on when the test is done. For example, first void of the day samples will yield the highest concentrations of drug metabolites. Testing urine at other times of the day will yield differing results, just as the concentration of urine itself changes throughout the day.

Due to these variations in urine concentration, positive test results can occur following a negative test result, although no additional cocaine was used. Many people try to avoid a positive test result by "watering up," or drinking large amounts of fluids to dilute their urine. Ideally, a 24-hour sample should be taken, but this is impossible in most work settings. Performing random urine sampling is about the only way to assure a representative specimen.

The widely accepted time period for benzoylecgonine to be cleared from the urine is three to five days. One study suggests that high dose users (i.e., 0.5 gram or greater for each episode of use) can test positive after eight days. Another study claims that benzoylecgonine can be detected in heavy cocaine users for 10-14 days. The longest time over which positive urine levels of benzoylecgonine were detected was 10-22 days. This was after chronic use of extremely high doses of 112 grams per week. Since it is usually difficult to determine exactly how much cocaine is being abused by a caller, it seems that a broader range of potential detection times should be given when explaining cocaine metabolism in regard to urine testing.