Background: Gamma-hydroxybutyric acid (GHB) is a recreational drug with central nervous system depressing effects that is often abused. A urine GHB point-of-care test can be of great diagnostic value. The objective of this prospective study was to determine the performance of the new DrugCheck GHB Single Test and the Viva-E GHB immunoassay for urine samples in emergency department patients. Methods: Patients presented to the emergency department of the OLVG hospital in Amsterdam with a Glasgow Coma Scale score ,15 and potential drug of abuse intoxication were included in the study. Between June 2016 and October 2017, 375 patients were included. Using the DrugCheck GHB Single Test (Express Diagnostics Int’l, Blue Earth, MN) and the Viva-E GHB immunoassay (Siemens Healthineers, The Hague, the Netherlands), patients’ urine samples were tested for GHB (cutoff for a positive result, 10 or 50 mcg/mL GHB). To ensure quality, the results obtained were compared with those generated using a validated gas chromatography method. The tests were considered reliable if specificity and sensitivity were both .90%. Possible cross-reactivity with ethanol was investigated by analyzing ethanol concentrations in patients’ samples. Results: Seventy percentage of the included patients was men, and the median age was 34 years old. The DrugCheck GHB Single Test’s specificity and sensitivity were 90.0% and 72.9%, respectively, and using 50 mcg/mL as a cutoff value, its specificity and sensitivity improved to 96.7% and 75.0%, respectively. Serum and urine ethanol levels in the false-positive group were significantly higher compared with those in the true-negative group. The specificity and sensitivity of the Viva-E GHB immunoassay (cutoff value of 50 mcg/mL and excluding samples with ethanol levels $2.0 g/L) were 99.4% and 93.5%, respectively. Conclusions: The DrugCheck GHB Single Test’s specificity was sufficient, whereas its sensitivity was poor, making it unsuitable for use at point-of-care. Contrarily, using 50 mcg/mL as the cutoff value and excluding samples with ethanol levels $2.0 g/L, the Viva-E GHB immunoassay showed acceptable results to detect clinically relevant GHB intoxications.

GHB, point-of-care, immunoassay, ethanol, emergency department,
Therapeutic Drug Monitoring

Smits, T.A., Gresnigt, F.M.J., van Groen, B, Franssen, E.J.F., & Attema-de Jonge, M.E. (2020). Prospective Investigation of the Performance of 2 Gamma-Hydroxybutyric Acid Tests: DrugCheck GHB Single Test and Viva-E GHB Immunoassay. Therapeutic Drug Monitoring, 42(1), 139–145. doi:10.1097/ftd.0000000000000677