METHODS

1. Ethylene Glycol Screening: Adapting the CATACHEM Enzymatic Assay to Minimize False PositivesLindsay Hardy1, Shu-Ling Fan1, Adele Pistorino1, JoEtta Juenke2, Gwendolyn McMillin3, Gary Horowitz11Department of Pathology, Beth Israel Deaconess Medical Center, Boston, MA, USA., 2ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT, USA, 3Department of Pathology, University of Utah, Salt Lake City, UT, USA. ABSTRACT INTRODUCTION: Ethylene glycol (ETG) is a toxic substance found in automotive anti-freeze. The most commonly used methods for quantification are gas chromatography (GC) with flame-ionization (FID) or mass spectrometry (MS). A veterinary medicine enzymatic assay, by CATACHEM, was previously noted for interfering substances, including propylene glycol (PG) and 1,3-butanediol (BD). OBJECTIVE: In this study, new method parameters for the CATACHEM assay were selected in an effort to minimize interferences and other sources of false positive results. RESULTS: 1) Recovery studies for both methods were linear as high as 250 mg/dL. Accuracy and precision tests revealed CV of: 3.4% at 61.7 mg/dL, 1.2% at 227.9 mg/dL. 2) Three analytes were tested for interference: glycerol, PG, and BD. Glycerol did not interfere with either method. PG and BD gave falsely elevated ETG results at all concentrations using the original method; neither compound gave falsely elevated ETG readings with the new method. 3) Twenty de-identified clinical samples with ethanol ordered were tested. Using the original method, five yielded ETG levels >10 mg/dL. Using the new method, all twenty samples were reported as <10 mg/dL of ETG. 4) For 13 clinical samples, the modified data reduction yielded 3 results with error messages, two of which were beyond the assay’s measuring range (~500 mg/dL). Compared to GC-FID, for the 10 samples without error messages, r-squared = 0.97. RESULTS Interfering Substances (BIDMC) Kinetics Patient Correlation Two Point End: Compares the absorbance at two time points Rate A: Measures the slope of the increased absorbance over many points • METHODS • METHOD: A bacterial enzyme, Glycerol Dehydrogenase, oxidizes ETG in the presence of NAD, causing the production of NADH and an increase in absorbance at 340 nm. Precision Data Buffer, Stabilizer Nonreactive ingredients Glycerol Dehydrogenase • In the presence of interfering substances, the new method generated either accurate results or flagged an error message, whereas the old method simply generated (erroneous) elevated values. • Overall, 67 samples were spiked either in combination or alone with: • ethylene glycol, propylene glycol, • formic acid, n-propanol, • isopropanol, acetone, • methanol, ethanol, • glycolic acid, polyethylene glycol, • oxalic acid, glyoxal solution, • glyoxylic acid, 1,2 butanediol, • 1,2 butanediol, 1,3 propanediol, • 1 butanol, 1,3 butanediol, • 1,4 butanediol, 1-octanol • In no case did the new method generate an erroneous result. Ethylene Glycol Glycoaldehyde NADH + H+ NAD+ Elimination of False Positives in Ethanol Samples CONCLUSIONS • The new method exhibits excellent agreement with the reference method (gas chromatography – flame ionization detection). • In contrast to the original method, no false positive ethylene glycol results were generated among the samples tested (patient and spiked). • The new method was successfully implemented at two sites, using two different instruments, with excellent agreement. • This new method may make it practical for many laboratories to offer accurate ethylene glycol determinations on routine chemistry instrumentation. Ethylene Glycol Parameters for Two Instruments