Some steroids can be analyzed with this technique, whereas HPLC and GC lack appropriate sensitivity to detect beta-adrenergic blockers. Antibodies that bind selectively to certain drugs or drug metabolites are chosen, and the sensitivity and the specificity of this test are only as good as the antibody chosen. The binding is proportional to the amount of drug in the urine and can be detected through enzymes, radioisotopes, or fluorescent compounds. With this technique, very small amounts of drug can be detected in a very small amount of urine, although this test may not differentiate between specific drugs within a class of drugs. The scintillation counter is used to measure the amount of radioactive particles present.
Radioactivity is inversely proportional to metabolite level.
RIA tests are a little more sensitive than the EMIT, and harder to beat. The EMIT is more common because RIA produces radioactive waste, and radioactive waste is difficult to deal with. Unfortunately, there is no standard procedure to expect. If you pass the EMIT, you're off the hook. Lewis Maltby, director of the Workplace Rights Office, said the EMIT test is wrong 25 to 30 percent of the time.