I Letter to the Editor Reagent Lot-to-Lot Variability in Sensitivity for Amphetamine with the Syva Emit I! Monoclonal Amphetamine/Methamphetamine Assay To the Editor:

The testing of urine samples for drugs of abuse is usually performed by first analyzing the samples with an immunoassay screen. There ar a number of immunoassays available for screening urine samples for amphetamines and methamphetamine (1). In general, the amphetamine assays screen for thegr up of drugs that comprises amphetamine, methamphetamine, a d other sympathomimetic amines. Different immunoassays for amphetamine have different crossreactivities to he ympathomimetic amines. Several factors need t be taken into consideration in the interpretation fa positive result for amphetamines by immunoassay. The issue of crossreactivity of sympathomimetic amines present in over-the-counter medication has been extensively covered in the literature(1,2). The amphetamine immunoassays are calibrated with eithermethamphetamine or amphetamine. These immunoassays are also known to have different sensitivity towards amphetamine and methamphetamine. Because of this variability, analysts using these immunoassays for amphetamine must understand the performance characteristics of the assays that they use. In screening urine samples, the immunoassays should be able to detect the presence of amphetamine and methamphetamine. The Department of Health and Human Services (HHS) guidelines for mployee drug-testing programs have a cutoff of 1000 ng/mL for the amphetamine immunoassay (3). Samples containing amphetamine, methamphetamine, or a combination of both drugs equivalent to a concentration of 1000 ng/mL are expected to produce a positive response