Use of a Reference Material Proposed by the International Federation of Clinical Chemistry and Laboratory Medicine to Evaluate Analytical Methods for the Determination of Plasma Lipoprotein(a)

Abstract

Background: As part of the NIH/National Heart, Lung and Blood Institute Contract for the Standardization of Lipoprotein(a) [Lp(a)] Measurements, a study was performed in collaboration with the IFCC Working Group for the Standardization of Lp(a) Assays. The aims of the study, performed with the participation of 16 manufacturers and 6 research laboratories, were to evaluate the IFCC proposed reference material (PRM) for its ability to transfer an accuracy-based value to the immunoassay calibrators and to assess concordance in results among different methods. Methods: Two different purified Lp(a) preparations with protein mass concentrations determined by amino acid analysis were used to calibrate the reference method. A Lp(a) value of 107 nmol/L was assigned to PRM. After uniformity of calibration was demonstrated in the 22 evaluated systems, Lp(a) was measured on 30 fresh-frozen sera covering a wide range of Lp(a) values and apolipoprotein(a) [apo(a)] sizes. Results: The among-laboratory CVs for these samples (6–31%) were, in general, higher than those obtained for PRM (2.8%) and the quality-control samples (14%, 12%, and 9%, respectively), reflecting the broad range of apo(a) sizes in the 30 samples and the sensitivity of most methods to apo(a) size heterogeneity. Thus, although all of the assays were uniformly calibrated through the use of PRM, no uniformity in results was achieved for the isoform-sensitive methods. Conclusions: Linear regression analyses indicated that to various degrees, apo(a) size heterogeneity affects the outcome of the immunochemical methods used to measure Lp(a). We have also shown that the inaccuracy of Lp(a) values determined by methods sensitive to apo(a) size significantly affects the assessment of individual risk status for coronary artery disease.

Functional approach to investigate Lp(a) in ischaemic heart and cerebral diseases

“…A normal value for plasma concentration has not been agreed upon: some authors consider this to be up to 20 mg dL − 1 [16] and others up to 30 mg dL − 1 [17], pointing out that the use of different monoclonal or polyclonal antibodies generates differences in results [18]. In order to assess concordance in results among different methods, a calibrator and a reference ELISA method have been evaluated and demonstrated to be insensitive to apo(a) isoform-size heterogeneity [19].…”

Lipoprotein(a), polymorphisms in the LPA gene, and incident venous thromboembolism among 21 483 women

“…Lp(a) measurement was performed in a core laboratory certified by the NHLBI/CDC Prevention Lipid Standardization Program. We used the only commercially available assay, not affected by Kringle IV-Type 2 repeats, as assessed by a NHLBI and International Federation of Clinical Chemistry standardization group [12]. The turbidimetric assay used reagents and calibrators from Denka Seiken (Niigata, Japan) on the Hitachi 917 analyzer (Roche Diagnostics, Indianapolis, IN, USA).…”

“…Strengths of this study include its prospective nature and use of a reliable mass-based assay [12] to measure circulating levels of Lp(a). Some of the prior discrepant findings of studies regarding Lp(a) levels and VTE may be due in part to difficulty in measuring Lp(a).…”

DNA- and Plasma-based Screening for Risk Factors in Infants and Children with Symptomatic Thromboembolism/DNA- und plasmabasiertes Screening von Risikofaktoren bei Säuglingen und Kindern mit symptomatischen thromboembolischen Ereignissen

“…Suitable protein-based assays for determination of APC-R [66,67], protein C, protein S and antithrombin activity, concentration of clottable fibrinogen, plasminogen activity, activities of coagulation factors VIIIC and XII, Lp(a) [68,69], histidine-rich glycoprotein, heparin cofactor II, and fasting homocysteine concentrations, should be investigated along with DNA-based assays, i. e. factor V G1691A mutation, prothrombin G20 210A variant and MTHFR C677T genotype.…”