Apolipoprotein standardization in multiple calibration laboratories requires equivalent results to value assign matrix-based reference and external quality assurance materials. A multiplexed LC-MS/MS- Show more
Apolipoprotein standardization in multiple calibration laboratories requires equivalent results to value assign matrix-based reference and external quality assurance materials. A multiplexed LC-MS/MS-based reference measurement procedure (RMP) has been developed for serum apolipoproteins apo(a), apoA-I, apoB, apoC-I, apoC-II, apoC-III, and apoE. This study evaluates the transferability of the RMP between 3 calibration labs and determines the between-laboratory imprecision. Six periodic ring trial surveys were held. The study protocol, calibrators, internal standards, quality controls (QCs), and clinical samples (CSs) were shared among the laboratories. Intra-laboratory imprecision and inter-peptide comparisons evaluated intra-laboratory performance, while inter-laboratory imprecision evaluated equivalence between the calibration labs. Precision of the common bilevel QC monitored the level of harmonization over time. Intra-laboratory imprecision fulfilled predefined analytical performance, defined as repeatability <50% of the maximum allowable uncertainty (MAU) at minimal criteria. Median interlaboratory variation (CVbl) was 3.71%, 3.33%, 7.38%, 6.74%, 3.88%, and 3.90% for apoA-I, apoB, apoC-I, apoC-II, apoC-III, and apoE, respectively. For apo(a), CVbl was concentration (x) dependent following 206.32×x-0.899%. In QC samples, the average imprecision for all apolipoproteins decreased from 6.0% and 18.1% for QC1 and QC2, to 5.2% and 9.5%, indicating improvement of analytical performance of the network over time. This study shows the feasibility of transferring the multiplex apo LC-MS/MS-based RMP between laboratories. Predefined performance specifications were fulfilled for all seven apolipoproteins. Ongoing round-robin studies will ensure stable performance of the calibration labs required to accomplish an accurate value-base for apolipoprotein certification of commercial reagents. Show less
Lipoprotein(a) (Lp(a)) has the reputation of being the most misunderstood metric in laboratory medicine. The unique apolipoprotein(a) (apo(a)) in Lp(a) is very heterogenous, the kringle IV domain of a Show more
Lipoprotein(a) (Lp(a)) has the reputation of being the most misunderstood metric in laboratory medicine. The unique apolipoprotein(a) (apo(a)) in Lp(a) is very heterogenous, the kringle IV domain of apo(a) being formed by 12-50 kringles due to 3 to ∼40 KIV Show less