Performance of Abusign drugs-of-abuse slide tests with particluar emphasis on concentrations near the cutoff: comparison with FPIA-ADx and confirmation of results with GC-MS.

The objective of the present study was to evaluate the performance of Abusign test slides in comparison with fluorescence polarization immunoassay (FPIA)-ADx and gas chromatography-mass spectrometry (GC-MS) confirmation with special emphasis on concentrations near the cutoff. Analysis was performed on 35 individual slide tests for cocaine (cutoff, 300 ng/mL), cannabinoids (cutoff, 100 ng/mL), and opiates (cutoff, 300 ng/mL); 104 tests for cannabinoids (cutoff, 50 ng/mL); and 34 panel slides (amphetamine cutoff 1000 ng/mL, cocaine cutoff 300 ng/mL, opiates cutoff 300 ng/mL, and cannabinoids cutoff 100 ng/mL). Urine samples that had a concentration measured with FPIA-ADx within +/-25% of the Abusign cutoff were selected. Inter- and intra-individual agreement were assessed from the readings of the slides (positive or negative) by four persons at t = 3, 5, and 10 min after sample incubation. In addition, the sensitivity and specificity of the cannabinoids slide test (50 ng/mL) were compared with those of FPIA-ADx using GC-MS as the gold standard. There was a considerable variation in the reading of the slides between different persons. In addition, for the same observer the reading could depend upon the time of incubation. In comparison with FPIA-ADx, the Abusign test slides showed a high sensitivity (46% vs. 87%) and a low specificity (95% vs. 51%). We concluded that the Abusign slide test is unsuitable for situations in which a reliable test result is desired because of the low interindividual agreement, the dependency of the test result upon time, and the low specificity. However, the test slides may be of value in toxicological screening.