Adulterants

In reference to urine testing for drugs of abuse (DOA), adulteration of a sample means the addition of some agent (salts, acids, oxidizers, or even water) to a urine sample to produce a falsely negative result. Adulteration is done to trick the clinician into thinking the patient has no drug present in their sample.

Adulterants are simple chemical additions that change the pH of the urine, oxidize or reduce proteins, or change the ionic environment such that the detection antibodies don't effectively bind the drugs that are present. Or the chemicals may inactivate the antibody-linked detection systems. Some adulterants that are used include:

Individuals also add bleach, hand soap, vinegar, or other common household items to their samples to interfere with the screening test. To combat the adulteration of samples, laboratory professionals should be aware of a sample with a strange smell or strange appearance. Ideally, the sample should be assessed by the collector within four minutes so that normal color, odor, foaming, the presence of any precipitates, and temperature can be checked. The temperature should be between 90–100° F (32–38° C). The pH should be between 4–11. There are urine dipsticks available, such as the example shown on the right, which test for the presence of adulterants. Some laboratories may choose to use these dipsticks to test pain management urine samples.

The most important tests for adulteration are urine creatinine and specific gravity. If the sample has a specific gravity of less than 1.005 or the urine creatinine is less than 20 mg/dL, adulteration of the sample should be suspected. Since it is easy for a patient to simply replace or dilute a specimen with tap water or toilet water, a creatinine value <20 should be considered an invalid specimen. The sensitivity of a drug screen on a sample with a value <20 mg/dL is very low.