Assessing Propylene Glycol Interference at Concentrations Relevant to Serum Levels With Electronic Cigarette Use in an Enzymatic Ethylene Glycol Assay

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Abstract Introduction Clinical laboratory measurement of ethylene glycol (ETG) by enzymatic methods is known to be subject to interference with high (several hundred milligrams/deciliter) concentrations of propylene glycol (PG). An estimated 10.8 million people in the United States, or almost 1 in 20 Americans, are reported to use electronic cigarettes (e-cigarettes; ie, “vaping”), in which PG is frequently used as a liquid solvent. No published reports exist investigating whether serum concentrations of PG that may be seen with e-cigarette use (generally, concentrations of 10-15 mg/dL in moderate users and up to 30 mg/dL in heavy users) can lead to either interference flags in analytical ETG measurement or falsely positive ethylene glycol concentrations being reported. Methods Studies were conducted to assess PG interference on enzymatic ETG measurement. Commercially acquired human AB serum (catalog # 35-060-CI; Corning Life Sciences) was spiked with various amounts of PG (catalog #158720010; Acros Organics/Thermo Fisher Scientific) to achieve both concentrations of PG expected with e-cigarette use (0-30 mg/dL) and supra-physiological concentrations (>30 mg/dL) for comparative purposes. PG-spiked sera were tested using a quantitative enzymatic ETG assay (Quantitative Ethylene Glycol kit, catalog #C504-0A; Catachem) previously validated as a laboratory-developed test on an AU5810 automated chemistry analyzer (Beckman Coulter). Results None of the tested PG concentrations designed to mimic physiological levels expected with e-cigarette use (0, 5, 10, 15, 20, 25, and 30 mg/dL) caused falsely positive quantitative ETG results, defined as values above the ETG limit of quantitation (LOQ) of 5 mg/dL. At these low concentrations, interference patterns neither were observed in reaction monitors, nor were instrument interference error flags triggered. As concentrations of PG approached 50 mg/dL, abnormal curve appearances were observed in the instrument reaction monitor, although this neither resulted in interference error flags nor false detection of ETG. However, as PG concentrations approached and exceeded ≥100 mg/dL, both interference flags and falsely positive ETG results were observed. Conclusion Results from the present experiments demonstrate that serum concentrations of PG expected with e-cigarette use did not cause interference with enzymatic ethylene glycol detection in this assay.