Ethylene glycol determination in serum: comparison between enzymatic assay and GC-MS on real samples

Ethylene glycol intoxication can be life-threatening, but clinical signs lack sensitivity and specificity. Hence, the diagnosis relies on the detection of this compound in serum. Chromatographic methods are the gold standard, but they are hard to routinely apply. As a result, we implemented an enzymatic assay on automated analyzers. The aim of this study is to review the results of real samples and compare both methods over 10 years.

The enzymatic assay relies on oxidation of ethylene glycol to glycolaldehyde. All results were confirmed by gas chromatography coupled to mass spectrometry. Both methods share a lower limit of quantification of 50 mg/L.

During the study period, 405 unique patient samples were analyzed: 305 samples tested negative by both methods (75.3% true negative) while 34 tested positive on both instruments (8.4% true positive). Only four samples tested negative by enzymatic assay were positive with chromatography (<1% false negative) and chromatography failed to confirm 62 samples that screened positive by enzymatic assay (15.3% false positive), yielding a sensitivity of 89% and a specificity of 83%.

The sensitivity and specificity of the enzymatic assay are high. Most of the false positive samples were below a treatment threshold (200 mg/L). Some false positive results could be explained by high blood concentrations of lactate and/or high lactate dehydrogenase activity but a small proportion remained unexplained. The main advantage of the enzymatic reagent is a significant reduction of turnaround times compared to chromatography.

A rapid enzymatic assay for ethylene glycol allows for quick adjustments to patient care, avoiding unnecessary treatment or, conversely, insufficient treatment. However, any positive result should be confirmed by chromatography and interpreted in the context of the patient's medical history and clinical findings.