Interpretation and Utility of Drug of Abuse Immunoassays: Lessons From Laboratory Drug Testing Surveys

Abstract

Abstract Context.—To assist with patient diagnosis and management, physicians from pain services, drug treatment programs, and the emergency department frequently request that urine be tested for drugs of abuse. However, urine immunoassays for drugs of abuse have limitations. Objective.—To use data from the College of American Pathologists Proficiency Testing Surveys to determine and summarize the characteristics, performance, and limitations of urine immunoassays for drugs of abuse. Design.—Six years of urine drug testing proficiency surveys were reviewed. Results.—Lysergic acid diethylamide and methaqualone are infrequently prescribed or abused and, therefore, testing may be unnecessary. However, implementation of more specific testing for methylenedioxymethamphetamine and oxycodone may be warranted. Each drug of abuse immunoassay exhibits a different cross-reactivity profile. Depending on the cross-reactivity profile, patients with clinically insignificant concentrations of drugs may have false-positive results, and patients with clinically significant concentrations of drugs may have false-negative results. Conclusions.—Laboratory directors should be aware of the characteristics of their laboratories' assays and should communicate these characteristics to physicians so that qualitative results can be interpreted more accurately. Furthermore, manufacturer's claims should be interpreted with caution and should be verified in each organization's patient population, if possible.