{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,14]],"date-time":"2026-11-14T04:53:54Z","timestamp":1794632034103,"version":"4.9.1"},"reference-count":23,"publisher":"Oxford University Press (OUP)","issue":"7","license":[{"start":{"date-parts":[[2026,4,18]],"date-time":"2026-04-18T00:00:00Z","timestamp":1776470400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"German Society for Clinical Chemistry and Laboratory Medicine"},{"DOI":"10.13039\/501100008799","name":"Foundation for Pathobiochemistry and Molecular Diagnostics","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100008799","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100016545","name":"Roche Diagnostics","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100016545","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000030","name":"US Center for Disease Control and Prevention","doi-asserted-by":"publisher","id":[{"id":"10.13039\/100000030","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,7,6]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Intra-laboratory imprecision fulfilled predefined analytical performance, defined as repeatability &amp;lt;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\u00d7x\u22120.899%. 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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>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.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/clinchem\/hvag020","type":"journal-article","created":{"date-parts":[[2026,2,23]],"date-time":"2026-02-23T12:26:00Z","timestamp":1771849560000},"page":"791-800","source":"Crossref","is-referenced-by-count":1,"title":["Transferability and Between Laboratory Imprecision of an LC-MS\/MS-Based Reference Measurement Procedure for Apolipoproteins"],"prefix":"10.1093","volume":"72","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3737-3807","authenticated-orcid":false,"given":"L Renee","family":"Ruhaak","sequence":"first","affiliation":[{"name":"Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center , Leiden ,","place":["the 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