STC Technologies, Inc., 1745 Eaton Avenue, Bethlehem, PA 18018, USA

The object of this study was to evaluate the STC Methamphetamine MICRO-PLATE EIA for oral fluid collected using the OraSure^® Oral Specimen Collection Device and compare it to the STC Methamphetamine MICRO-PLATE EIA for urine. The analytical sensitivity was evaluated by determining the LOD (Limit of Detection), which is defined as the average signal-noise ratio of the 0 ng/mL concentration (A₀) minus the noise times three (LOD = A₀ - 3SD). The oral fluid EIA LOD is 1.0 ng/mL, and the urine EIA LOD is 50 ng/mL. A study on the effects of sample pH determined that an oral fluid pH of 3, 4, or 5 caused false positives at a 10 ng/mL cutoff, but in the urine no effect of pH was found. Cross-reactivity studies involved 48 ubiquitous cross-reactants (10,000 ng/mL concentration), none of which produced a positive result in both assay formats, and 16 analogous cross-reactants. The following data for analogous cross-reactants is expressed in % cross-reactivity (oral fluid/urine, nd = not detected): L-methamphetamine (145/262), MDMA (358/827), MDA (1.1/3.4), B-phenethylamine (nd/0.22), D-amphetamine (nd/0.55), diphenhydramine (0.009/0.15), fenfluramine (5.7/1.0), isoxsuprine (nd/1.5), L-ephedrine (0.97/0.99), L-phenylalanine (nd/0.78), mephentermine (1.3/0.37), phentermine (0.07/0.1), phenylephrine (0.1/0.28), phenylpropanolamine (nd/0.19), procaine (0.07/0.16), and pseudoephedrine (1.3/1.5). The precision studies using 0, 5, 10, and 20 ng/mL oral fluid calibrators indicate intra-assay % CV of 8.3, 11.8, 10.5, and 11.4, and inter-assay % CV 4.2, 6.7, 10.6, and 8.1, respectively.

Eighty-one (81) matching saliva and urine clinical specimens (57 from self-reported, methamphetamine users and 24 from non-users) were tested with EIA and GC/MS (LOQ = 1 ng/mL). Thirty-nine (39) oral fluid specimens and 41 urine specimens were negative by GC/MS using a 10 ng/mL cutoff for oral fluid and a 500 ng/mL cutoff for urine. The oral fluid EIA detected 39 true negatives and 42 true positives; therefore, the percent sensitivity and specificity for the EIA oral fluid versus GC/MS were determined to be 100% and 100%, respectively.