Comparison of Qualitative and Quantitative Clinical Assays in Suspected Ethylene Glycol Exposure Open Access

Schwartz, Michael (2014)

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Background: Availability of rapid analysis for suspected ethylene glycol (EG) exposure remains an unmet need in medical toxicology practice. Ethylene glycol poisoning is a significant source of morbidity and mortality in the U.S. with over 5000 cases of poisoning reported each year to poison control centers. Mass poisonings from methanol-tainted liquor and ethylene and diethylene glycol-contaminated pharmaceuticals have occurred worldwide. Lack of a clinical assay for EG exposure leads to presumptive therapy with expensive antidotes and consumption of hospital resources until the diagnosis can be confirmed. Objective: To evaluate the assay performance (sensitivity, specificity, positive predictive value, negative predictive value, correlation) of a i) veterinary point-of-care (POC) qualitative (colorimetric) EG test kit and an ii) enzymatic, chemistry auto-analyzer-based quantitative EG assay. Methods: We conducted a cross sectional study (n=56) of the REACT EGT kit (Allelic Biosystems, Kearneyville, WV) and the ZBx LQ Ethylene Glycol Assay (Clinitox Diagnostics, Ontario, Canada) on cases of suspected EG intoxication referred to our poison center. Assay results were compared to criterion standard testing for EG exposure using gas chromatography/mass spectrometry. Results: The colorimetric assay lacked specificity for true EG exposure; multiple interferences preclude its clinical utility. The ZBx LQ Ethylene Glycol assay performed with 100% sensitivity and 100% specificity for clinically significant EG exposure (range of EG serum concentrations 6.3 to 620 mg/dl). Method comparison of the assay with GC/MS demonstrated excellent correlation (r=0.9803; p=0.000). Discussion: The ZBx LQ Ethylene Glycol assay's performance, ease of adaptability to a hospital clinical laboratory's chemistry platform, and low cost, make it useful for the rapid laboratory diagnosis of EG exposure. The sample size in our study was small; a larger, pivotal study and eventual regulatory approval are required before the assay becomes widely available. Conclusion: The ZBx LQ Ethylene Glycol assay fills a significant gap in the routine availability of reliable EG clinical testing.

Table of Contents

Introduction and Background 1

Methods 6 Results 10 Discussion 14 Conclusion 21 References 22

Tables and Figures 23

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