Evaluation of the Abbott ADx Amphetamine/Methamphetamine II Abused Drug Assay: Comparison to TDx, EMIT, and GC/MS Methods

Although the legitimate clinical use of amphetamine and amphetamine congeners is declining, the illicit use of these drugs remains high. There is a need for a rapid and conclusive method for detecting these compounds in routine urine drug testing, drug screening in drug rehabilitation centers, and as an aid in the diagnosis and treatment of potential overdoses. The Abbott ADx™ Amphetamine/Methamphetamine II assay (A/M II), a fluorescence polarization immunoassay (FPIA), was compared to the Abbott TDx® Amphetamine/Methamphetamine II assay (FPIA), the Syva enzyme-multiplied immunoassay technique (EMIT) and a gas chromatograph/mass spectrometry (GC/MS) method. Precision of the A/M II assay was evaluated on the ADx analyzer over a 14-day period in each of three modes of operation (batch, combination, and panel) and was based on within-run and between-run coefficients of variation (CVs). Within-run CVs for all three controls (low [L], medium [M], and high [H]) ranged from 0.40% to 10.60% and between run CVs ranged from 3.96% to 7.92%. Data indicated that the calibration curve was stable for 16 days. Each of the six calibrators and three controls were within 10% of their labeled concentrations when analyzed by GC/MS. Fifty routine clinical specimens from our laboratory and 74 specimens screened as positive for amphetamine or related compounds from a rehabilitation center were screened by ADx, TDx, and EMIT. Any specimen yielding a positive result by any of these three methods was confirmed by GC/MS. In-house controls, as well as clinical samples, which contained both amphetamine and methamphetamine in the same sample produced results greater than two times the expected response on the ADx and TDx. Since these drugs may be present together in a patient sample, accurate quantitation of either or both drugs can only be accomplished by more specific analytical methodology.