36 Free Glycerol Measurement Reveals Triglyceride Bias With Limited Categorical Impact

This is the authors' abstract. We don't add key points for this paper.

Patients with elevated free glycerol may have falsely increased triglyceride (TG) concentrations leading to pseudo- hypertriglyceridemia. Enzymatic TG assays quantify glycerol released following triglyceride hydrolysis and do not correct for circulating free glycerol. Following discontinuation of commercially available glycerol blanked TG assay, we validated a method to directly measure free glycerol. The objective of this study was to determine the impact of glycerol correction on TG interpretation. Residual blood specimens from clinically ordered hemoglobin A1 C (HbA1c) and TG were measured for free glycerol (n = 272). HbA1c was measured using ion exchange HPLC, on the Bio-Rad D-100 analyzer. Roche Cobas c501 (Indianapolis, IN) was used to measure TG (TRIGL, Roche) and free glycerol (GLYC, Randox). Corrected TG was calculated by converting TG to mmol/L and subtracting the free glycerol concentration. Corrected TG > 10mg/dL were defined as clinically meaningful. Free glycerol exhibited a right skewed distribution; overall 16.4% of specimens were above the reference interval (114 mcmol/L). The median (IQR) concentration of glycerol was significantly higher in samples with elevated TG (>150 mg/dL),77.0 (54.1–101.3) mcmol/L vs. 54.0 (36.0–89.0) mcmol/L (p < 0.001). Median glycerol concentrations significantly increased with HbA1c categories including normal, Prediabetes and diabetes (<5.7%, 5.7–6.4% and ≥ 6.5%), (55, 74, and 84) mcmol/L, respectively; p = 2.9 × 10⁻⁶). HbA1c values were higher in specimens with elevated glycerol (p < 0.001). These patterns were consistent across sexes. Correction for glycerol reduced measured TG concentrations by a median (IQR) of 5.4 (3.5–8.7) mg/dL mg/dL overall. The median TG correction for samples with normal TG (<150 mg/dL) was 4.8mg/dL compared to 6.8mg/dl for those with elevated TG (>150 mg/dL) () (p = 0.001). However, only 2.6% of cases passed the clinical TG cutoff of 150 mg/dL after correction. Median TG correction increased with HbA1c category (4.4, 7.1, 7.9, p < 0.01) with 1.8%, 7.5% and 0% of patients being recategorized as TG < 150mg/dL. When restricting the analysis to samples with elevated measured triglycerides (≥150 mg/dL), glycerol correction reclassified triglycerides to < 150 mg/dL in 3.7% of patients with elevated HbA1c (2/54) and 1.8% of patients with normal HbA1c (1/55). Our data confirm previous reports of elevated free glycerol among patients with hypertriglyceridemia. Furthermore, while glycerol associated bias is common, its effect on categorical triglyceride classification is limited. Elevated HbA1c is associated with greater magnitude of triglyceride correction, but reclassification across the 150 mg/dL threshold occurs in only a small subset of patients. Direct measurement of glycerol provides important clinical context for interpreting elevated or borderline triglycerides and supports a targeted testing strategy to identify pseudo hypertriglyceridemia. This could improve result interpretation and promote appropriate laboratory practice, diagnostic accuracy and patient care.