Validation of a lipoprotein(a) particle concentration assay by quantitative lipoprotein immunofixation electrophoresis.

Background: Low-density lipoprotein (LDL) particle (P, or molar) concentration has been shown to be a more sensitive marker of cardiovascular disease (CVD) risk than LDL cholesterol. Although elevated circulating lipoprotein(a) [Lp(a)] cholesterol and mass have been associated with CV risk, no practicable method exists to measure Lp(a)-P. We have developed a method of determining Lp(a)-P suitable for routine clinical use.

Methods: Lipoprotein immunofixation electrophoresis (Lipo-IFE) involves rigidly controlled electrophoretic separation of serum lipoproteins, probing with polyclonal apolipoprotein B antibodies, then visualization after staining with a nonspecific protein stain (Acid Violet). Lipo-IFE was compared to the Lp(a) mass assay for 1086 randomly selected patient samples, and for 254 samples stratified by apo(a) isoform size.

Results: The Lipo-IFE method was shown to be precise (CV <10% above the 50 nmol/l limit of quantitation) and linear across a 16-fold range. Lipo-IFE compared well with the mass-based Lp(a) assay (r=0.95), but was not affected by variations in apo(a) isoform size. With a throughput of 100 samples in 90 min, the assay is suitable for use in the clinical laboratory.

Conclusions: The Lipo-IFE method will allow Lp(a)-P to be readily tested as a CVD risk factor in large-scale clinical trials.