Robust and Accurate 2-Year Performance of a Quantitative Mass Spectrometry-Based Apolipoprotein Test in a Clinical Chemistry Laboratory

To the Editor: We previously described a multiplex liquid chromatography–mass spectrometry (LC-MS)1 method for the quantification of 6 apolipoproteins (apo): A-I, B, C-I, C-II, C-III, and E (1). Analytical method validation was performed according to the Clinical and Laboratory Standards Institute (CLSI) protocols, and the intraassay CVs were 2.3% to 5.5% and total CVs were 2.5% to 5.9%. Moreover, results were interchangeable with immunoturbidimetric assays for apo A-I (Deming slope, 1.014) and for apo B-100 (Deming slope, 1.016) (1). Our laboratory-developed test has now been used intermittently during a 2-year period in various studies on clinical cohorts. Here we demonstrate the robustness and analytical performance of mass spectrometry-based apolipoprotein quantification using stable isotope dilution and multiple reaction monitoring (SID-MRM) on a triple quadrupole for routine practice in clinical laboratories. To evaluate performance of the LC-MS test with regard to precision and bias of test results, 2 native serum pools were included as internal quality control (QC) on each of the 96-well plate batches analyzed (both in triplicate) over this period. The measurements were compared with assigned values to assess bias and precision by analysis of repeated QC observations in …