Harmonization of Lipoprotein(a) Immunoassays with the IFCC- Endorsed Reference Measurement Procedure Validated in
Keita Yamashita1,2,3, Mitsuru Wakita4, Noriyasu Niizeki1
1Department of Laboratory Medicine, Hamamatsu University School of Medicine.
Aim:
Lipoprotein(a) [Lp(a)] is an independent risk factor for cardiovascular disease (CVD); however, the goal of resolving its measurement issues remains unachieved. Expanding on the "first step" by Miida et al., this study evaluated the feasibility of harmonizing Lp(a) measurements using an IFCC endorsed mass spectrometry-based reference measurement procedure (MS-RMP)-assigned serum panel across a broader range of reagents and CVD patient sample types.
Methods:
Eleven immunoassays were evaluated using 536 serum samples (including 416 patients with CVD). Mass-to-molar (nmol/L) conversion equations were derived using the IFCC-MS-RMP-assigned CDC serum panels. For high-concentration samples (170-600 nmol/L), the accuracy was validated through a direct comparison with isoform-insensitive MS-RMP and physiological saline test results.
Results:
All reagents showed a strong correlation (rs＞0.967) with the MS-RMP in the CDC panel. Inter-reagent differences in patient samples, up to 5.3-fold in mass units, were significantly reduced after molar conversion. High-concentration samples showed a good correlation (rs = 0.904) between MS-RMP and the current immunoassay (Roche), elucidating the bias characteristics relative to the isoform-independent reference method. Furthermore, the measurements were acceptable (within 5% error) up to 3-fold physiological saline, whereas reagent-specific variability increased at higher dilution ratios and in samples with extremely high analyte concentrations.
Conclusion:
Expanding on previous findings, the implementation of a serum panel assigned by the IFCC-MS-RMP significantly strengthens the harmonization of Lp(a) measurements. Precise validation using MS-RMP as a benchmark, even in the high-concentration range, provides a robust foundation for international standardization and the establishment of common clinical decision values.
