Effect of piperacillin-tazobactam on clinical capillary zone electrophoresis of serum proteins.

immunoassay, whereas the Syva and Genix assays are one-step immunochromatographic assays for rapid detection of opiates in urine with a cutoff concentration of 300 mg/L. Information about rifampin cross-reactivity with these immunoassays was not available from the manufacturers. The only reported interference for rifampin is with the opiates kinetic interaction of microparticles in solution (KIMS) method for Roche reagents on Cobas Integra (3, 4). The antibiotic rifampin is usually part of the treatment of tuberculosis, especially in patients with concomitant human immunodeficiency virus infection. Generally, drug abuse in some of these patients necessitates screening for opiates (4 ). In addition, in cases of mental confusion associated with tuberculous meningitis or rifampin toxicity, it is not uncommon for a drugs of abuse screen to be ordered. Depending on the specificity of the method, rifampin interference could be the cause of falsepositive opiate screening results. Therefore, the presence of rifampin treatment mandates confirmatory testing for opiates because it can interfere with the predictive value of certain rapid screening assays (5 ). We recommend that each laboratory evaluates rifampin interference with the opiates immunoassay in use. In addition, each laboratory should maintain an updated listing of reported interference problems with immunoassays, as part of a quality assurance program, and disseminate this information to the medical community (6). However, this rapid screen serves the need for emergency drug testing, but it must always be complemented by confirmation.