Testing
Lp(a) molar-to-mass conversion ratios vary two to three-fold by assay and isoform, a study of 1635 samples across 5 commercial tests (J Clin Lipidol 2018)
Original title: Relationship of lipoprotein(a) molar concentrations and mass according to lipoprotein(a) thresholds and apolipoprotein(a) isoform size
Researchers compared Lp(a) molar concentration (nmol/L) with Lp(a) mass (mg/dL) across various Lp(a) thresholds and apolipoprotein(a) isoform sizes, using 1635 samples measured by 5 commercial mass assays (two Denka assays of 80 samples each, two turbidimetric assays of 2545 and 2673 samples, and an ELISA of 2605 samples). Mean molar-to-mass ratios were 2.42 for one reference lab comparison, 1.64 and 2.02 for two Denka assays, and these ratios increased with Lp(a) level, from 1.82, 1.52 and 1.87 respectively below 75 nmol/L to 2.80, 1.89 and 2.24 above 125 nmol/L. Across commercial turbidimetric and ELISA assays, ratios ranged from below 1 to above 5. The findings show Lp(a) molar-to-mass ratios depend on the Lp(a) threshold, assay method and isoform size, so a single conversion factor between assays is inappropriate, supporting a shift toward molar concentration reporting for Lp(a).
Original abstract
Background: Lipoprotein(a) [Lp(a)] is reported as Lp(a) particle mass (mg/dL) or molar concentration of apolipoprotein(a) [apo(a)] (nmol/L), which is considered the gold standard. Values are often converted from one measurement to the other but the validity of this is unknown.
Objectives: To quantify the relationship between Lp(a) molar concentration and Lp(a) mass in the context of various Lp(a) level thresholds and apo(a) isoform size.
Methods: In all samples, Lp(a) levels in molar concentration and apo(a) isoform size were determined at the Northwest Lipid Metabolism and Diabetes Research Laboratories (NLMDRL). Lp(a) mass levels were determined at the University of California, San Diego (UCSD) (1635 samples), by 5 commercially available assays: Denka 1 and Denka 2 (each 80 samples), 2 turbidimetric assays (2545 and 2673 samples, respectively), and an enzyme-linked immunosorbent assay (2605 samples). The ratios between Lp(a) molar concentration and mass (eg, nmol/L/mg/dL) were calculated and related to apo(a) isoform size.
Results: The mean (SD) ratios for NLMDRL/UCSD, NLMDRL/Denka1, and NLMDRL/Denka2 were 2.42 (1.25), 1.64 (0.18), and 2.02 (0.22), respectively. The ratios for NLMDRL/UCSD, NLMDRL/Denka1, and NLMDRL/Denka2 increased by Lp(a) cutoffs, with ratios of 1.82, 1.52, and 1.87, respectively, for Lp(a) < 75 nmol/L and 2.80, 1.89, and 2.24, respectively, for Lp(a) > 125 nmol/L. For the commercial turbidimetric assays and enzyme-linked immunosorbent assay, the ratios ranged from <1 to >5.
Conclusions: Lp(a) molar/mass ratios are threshold, method, and isoform dependent. A single conversion factor between assays is not appropriate. These data support the transition of Lp(a) mass assays to molar concentration to improve diagnostic and clinical interpretation of Lp(a)-mediated risk.
Summary written by lp-a.org from the published abstract; figures as published. Page updated 18 August 2026. Methods.