{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,26]],"date-time":"2026-09-26T02:45:52Z","timestamp":1790390752583,"version":"4.1.0"},"reference-count":13,"publisher":"Walter de Gruyter GmbH","issue":"10","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2018,9,25]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec id=\"j_cclm-2018-0116_s_999_w2aab3b7d101b1b6b1aab1c15b1Aa\">\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>For the analysis of 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine ribonucleotides (6-MMPR), no external quality assessment scheme (EQAS) is currently available and no quality control samples can be made because of the absence of pure substances. An experimental design is tested to compare laboratory analytical results.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec id=\"j_cclm-2018-0116_s_998_w2aab3b7d101b1b6b1aab1c15b2Aa\">\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>In this EQAS, participating laboratories were asked to select patient samples from their routine analysis and exchange these with a coupled laboratory. Because of large differences in results between laboratories, all standard operating procedures were reviewed, revealing that the origin of these differences could be in the method of hydrolysis and the preparation of calibrators. To investigate the contribution of the calibrators to these differences, one participating laboratory was asked to prepare a batch of calibrators to be shipped to the participating laboratories for analysis.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec id=\"j_cclm-2018-0116_s_997_w2aab3b7d101b1b6b1aab1c15b3Aa\">\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Results for 6-TGN differed more between laboratories, compared with results for 6-MMPR. For 6-TGN and 6-MMPR 43% and 24% of the results, respectively, were out of the 80%\u2013120% range. When correcting the results from the exchange of the patient samples with the results of the calibrators, the mean absolute difference for 6-TGN improved from 24.8% to 16.3% (p&lt;0.001), while the results for 6-MMPR worsened from 17.3% to 20.0% (p=0.020).<\/jats:p>\n               <\/jats:sec>\n               <jats:sec id=\"j_cclm-2018-0116_s_996_w2aab3b7d101b1b6b1aab1c15b4Aa\">\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>This first EQAS for thiopurine drugs shows that there is a difference between laboratories in the analysis of 6-TGN, and to a lesser extent in the analysis of 6-MMPR. This difference for 6-TGN can partially be explained by the use of in-house-prepared calibrators that differ among the participants.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1515\/cclm-2018-0116","type":"journal-article","created":{"date-parts":[[2018,8,15]],"date-time":"2018-08-15T07:58:48Z","timestamp":1534319928000},"page":"1715-1721","source":"Crossref","is-referenced-by-count":6,"title":["A design for external quality assessment for the analysis of thiopurine drugs: pitfalls and opportunities"],"prefix":"10.1515","volume":"56","author":[{"given":"Karen","family":"Robijns","sequence":"first","affiliation":[{"name":"Dutch Foundation for Quality Assessment in Medical Laboratories (SKML), Section Therapeutic Drug Monitoring and Clinical Toxicology (KKGT), PO Box 43100, NL 2504 AC , The Hague , The Netherlands"},{"name":"Central Hospital Pharmacy , The Hague , The Netherlands"},{"name":"Haga Teaching Hospital , The Hague , The Netherlands"},{"name":"CAPHRI School for Public Health and Primary Care, Maastricht University , Maastricht , The Netherlands"},{"name":"Department of Clinical Pharmacy and Toxicology , Maastricht University Medical Centre+ , Maastricht , The Netherlands , Phone: +31-70-3217217, Fax: +31-70-3080140"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Matthijs","family":"van Luin","sequence":"additional","affiliation":[{"name":"Dutch Foundation for Quality Assessment in Medical Laboratories (SKML), Section Therapeutic Drug Monitoring and Clinical Toxicology (KKGT) , The Hague , The Netherlands"},{"name":"Department of Clinical Pharmacy , Rijnstate Hospital , Arnhem , The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rob T.P.","family":"Jansen","sequence":"additional","affiliation":[{"name":"Dutch Foundation for Quality Assessment in Medical Laboratories (SKML) , Nijmegen , The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cees","family":"Neef","sequence":"additional","affiliation":[{"name":"CAPHRI School for Public Health and Primary Care, Maastricht University , Maastricht , The Netherlands"},{"name":"Dutch Foundation for Quality Assessment in Medical Laboratories (SKML), Section Therapeutic Drug Monitoring and Clinical Toxicology (KKGT) , The Hague , The Netherlands"},{"name":"Department of Clinical Pharmacy and Toxicology , Maastricht University Medical Centre+ , Maastricht , The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daan J.","family":"Touw","sequence":"additional","affiliation":[{"name":"Dutch Foundation for Quality Assessment in Medical Laboratories (SKML), Section Therapeutic Drug Monitoring and Clinical Toxicology (KKGT) , The Hague , The Netherlands"},{"name":"University of Groningen, University Medical Center Groningen , Department of Clinical Pharmacy and Pharmacology , Groningen , The Netherlands"},{"name":"University of Groningen, Groningen Research Institute of Pharmacy , Department of Pharmacokinetics Toxicology and Targeting , Groningen , The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"374","published-online":{"date-parts":[[2018,8,15]]},"reference":[{"key":"2021021301061621438_j_cclm-2018-0116_ref_001_w2aab3b7d101b1b6b1ab2b1b1Aa","doi-asserted-by":"crossref","unstructured":"Moreau AC, Paul S, Del Tedesco E, Rinaudo-Gaujous M, Boukhadra N, Genin C, et al. 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