Impact of adulterants on RIA analysis of urine for drugs of abuse.

The effect of various adulterants on radioimmunoassay (RIA) tests for amphetamine, cannabinoids, cocaine (metabolite), phencyclidine (PCP), barbiturate, and morphine was evaluated. A total of 16 readily available agents, at concentrations ranging from 1 to 25%, were tested with negative and positive urine samples. The results demonstrate that both false positive and false negative RIA results can be produced by easily achievable levels of different agents in urine specimens. Of the RIA tests evaluated, the one for cannabinoids was most sensitive to the presence of adulterants, whereas the PCP assay was most resistant. Although the presence of some adulterants could be detected by measuring the pH or specific gravity of the urine, other agents, at concentrations sufficient to alter the RIA results, could not be as easily detected. Gas chromatography/mass spectrometry (GC/MS) analysis of adulterated samples with false positive RIA results showed no detectable drug, indicating that the adulterants interfered with the RIA test itself. In contrast, GC/MS analysis of samples with false negative RIA results confirmed that at least some adulterants acted by reducing the drug concentrations in the specimen.