Response to a Report on False-Positive Results in a Methadone Enzyme Immunoassay

In a recent technical brief, Lichtenwalner et al. (1) described their observation of false-positive results, caused by verapamil, in an immunoassay for methadone (Diagnostic Reagents, Inc.). The reagents used in this investigation (lot nos. 5E059, 5M112, 6E083, and 6M174) were manufactured during 1995 and 1996, based on the lot numbers disclosed by the investigators. We would like to report that such false-positive results have been corrected since June 1997 with the incorporation of a new monoclonal anti-methadone antibody. It is well understood that the specificity of immunological assays may …