Initial Test Cutoff Selection Based on Regression Analysis of Initial Test Apparent Analyte Result vs GC/MS Test Analyte Result—Evaluation of Two Radioimmunoassay Kits’ Test Data

Abstract

Current workplace drug-testing programs require reporting positive results only if the gas chromatography/mass spectrometry (GC/MS) results are at or above a cutoff concentration and the mandated initial immunoassay results are also at or above an identical or higher cutoff value. Because immunoassays are generally also responsive to compounds that are structurally related to the analyte, whereas GC/MS analysis is specific for individual compounds, the cutoff adopted for the immunoassay is generally set higher than that adopted for the GC/MS test. The corresponding immunoassay cutoff adopted for the immunoassay may be correlated to that adopted for the GC/MS test if: (a) the drug of abuse is a mixture of structurally related compounds or (b) multiple structurally related metabolites are produced as a result of drug exposure. We have previously demonstrated that the apparent 11-nor-Δ9 - tetrahydrocannabinol-9-carboxylic acid (9-THC-COOH) concentrations (derived from immunoassays) that statistically correspond to a specific 9-THC-COOH concentration (determined by GC/MS) varied with the immunoassay methodologies used [1] and with the reagent manufacturing dates [2] . In the current study, we evaluate empirical data derived from two RIA kits based on the same technology and available at the same time period, but supplied by two different manufacturers . Analytical procedures for …