B-291 Evaluation of Immunalysis Carisoprodol Metabolite / Meprobamate Urine Homogeneous Enzyme Immunoassay (HEIA) on the AU5800

Abstract Background Carisoprodol is a muscle relaxant, that metabolizes to meprobamate, a compound with sedative and anxiolytic characteristics. Sensitive and specific detection of these drugs in urine is important for monitoring medication adherence. This investigation aimed to validate the Immunalysis Carisoprodol Metabolite / Meprobamate Urine HEIA (331UR) on the Beckman AU 5800, by assessing specificity, sensitivity, precision, stability, and comparison to the validated Immunalysis Carisoprodol Urine Enzyme Immunoassay (331). This validation was required due to a manufacturer reagent reformulation that included switching the antibody source from rabbit to sheep. The new formulation had a change in cutoff for meprobamate cross-reactivity from 70 ng/mL to 280 ng/mL while maintaining the carisoprodol cross-reactivity at 100 ng/mL. Methods A total of 73 urine samples (34 negative and 39 positive) were tested using both Immunalysis Carisoprodol assays (331UR and 331) on the Beckman AU. Of these 73 samples, 59 were created using blank urine pools spiked with concentrations of carisoprodol above and below the assay cutoff of 100 ng/mL. These 59 contrived samples were compared to their assumed spiked concentrations. All other samples (n=14) were residual, de-identified samples previously tested for carisoprodol and meprobamate by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Specificity and sensitivity were measured with a minimum threshold of 90% qualitative agreement. Precision was evaluated for the Carisoprodol 331UR by analyzing 25 replicates of both positive and negative control samples over five days. Reagent stability was evaluated up to 15 days uncapped and onboard the analyzer. Sample carryover was assessed by analyzing a sequence of high positive and negative patient pools. Results The Carisoprodol 331UR demonstrated 100% specificity, correctly identifying all 34 negative urine samples, and 100% sensitivity, accurately detecting all 39 positive urine samples. This was an improvement over the existing assay that showed a 100% specificity but 97.4% sensitivity, falsely identifying 1 positive sample as negative. Precision testing performed using Carisoprodol 331UR positive control resulted in total %CVs ranging from 1.4% to 2.5% and precision testing performed using the low control resulted in total %CVs ranging from 3.0% to 3.5%. The Carisoprodol 331UR assay demonstrated acceptable reagent stability (percent change between -3.98% to 4.86%) when the reagent cartridge was uncapped and onboard the analyzer up to 14 days. Sample carryover studies conducted by testing repeated sequences of a high concentration (2494 ng/mL) carisoprodol sample followed by multiple replicates of a negative sample demonstrated no significant sample carryover. Conclusion Our evaluation of the Immunalysis Carisoprodol Metabolite / Meprobamate Urine HEIA on the Beckman AU 5800 demonstrates satisfactory specificity, sensitivity, and precision for detecting carisoprodol and its metabolite meprobamate in urine. The new formulation performs comparably to the current assay and can seamlessly replace the Carisoprodol 331 assay without significantly impacting testing performance.