Correlation and Commutability Study between an LC-MS-Based Reference Measurement Procedure and Immunoassays Measuring Apolipoprotein A-I and Apolipoprotein B

BACKGROUND: Serum concentrations of apolipoprotein A-I (ApoA-I) and apolipoprotein B (ApoB) can have a predictive value for cardiovascular events beyond the traditional lipid profile. The IFCC Working Group on Apolipoproteins by Mass Spectrometry is developing a novel reference measurement system for seven clinically relevant apolipoproteins, including ApoA-I and ApoB. The system will consist of a multiplex mass spectrometry-based reference measurement procedure (RMP) and commutable secondary reference materials (RMs). METHODS: Agreement between the RMP and 8 immunoassay-based measurement procedures (MPs) was investigated using 30 clinical samples. Furthermore, the commutability of 8 candidate RMs, consisting of frozen serum pools, and the existing WHO-IFCC standards SP1-01 and SP3-08 was assessed. RESULTS: The harmonization level among eight immunoassay-based MPs for ApoA-I and ApoB still needs improvement. The RMP results showed a good correlation with results of the immunoassay-based MPs for both ApoA-I and ApoB. For ApoA-I, 7 candidate RMs showed good commutability, while SP1-01 and one candidate RM showed potential noncommutability for one method comparison. For ApoB, the commutability profile of the candidate RMs was more variable, and SP3-08 showed noncommutability for several method comparisons. CONCLUSIONS: The RMP and the immunoassay-based MPs have comparable selectivity for ApoA-I and ApoB, and a well-established reference measurement system can lead to improved harmonization. Future commutable secondary RMs can be based on frozen human serum pools; however, for ApoB, preselection of single-donor samples might be needed to limit the impact of sample-specific effects.