Clinical utility of the lipemic index for identifying severe triglyceride-rich lipoprotein disorders in adults undergoing routine blood testing

BACKGROUND: The lipemic index (L-index) is an automated measure of plasma turbidity used for pre-analytical quality control in clinical chemistry. As turbidity often reflects accumulation of triglyceride-rich lipoproteins (TRL), elevated L-index values may indicate underlying hyperlipoproteinemias, including severe hypertriglyceridemia and familial dysbetalipoproteinemia (FD). These rare, underdiagnosed disorders can have severe clinical consequences such as pancreatitis and cardiovascular disease. OBJECTIVE: This study evaluated the clinical utility of the L-index for identifying severe TRL disorders in adults undergoing routine blood testing. METHODS: In this cross-sectional study, all samples with an L-index result were eligible, except pediatric and ICU samples. In patients with L-index ≥1, a lipid panel and apoB were measured in leftover material. After excluding patients receiving intravenous lipid emulsions, patients with dyslipidemia were screened for severe TRL disorders (severe hypertriglyceridemia [>10 mmol/L] or an FD-like phenotype [TG ≥2.0 mmol/L, TC ≥5.2 mmol/L and non-HDL-C/apoB >3.69]). FD-like phenotypes were assessed using polyacrylamide gradient gel electrophoresis (PGGE). RESULTS: Among 332,476 consecutive samples from 71,768 unique patients, 575 patients (0.8%) had L-index ≥1, of whom 441 (77%) had dyslipidemia. Among patients with L-index ≥1 and dyslipidemia, 154/441 (35%) met biochemical screening criteria for a severe TRL disorder. PGGE confirmed an FD-like phenotype in 2/20 (10%) cases. CONCLUSION: Although the prevalence of an elevated L-index was low, approximately one-third of patients with L-index ≥1 and dyslipidemia met biochemical screening criteria for a severe TRL disorder. As an automated measure available at no additional cost, the L-index may help identify patients warranting further evaluation, particularly for severe hypertriglyceridemia and potentially FD-like phenotypes.