{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T20:34:36Z","timestamp":1788554076462,"version":"build-2803163510"},"reference-count":23,"publisher":"Oxford University Press (OUP)","issue":"4","license":[{"start":{"date-parts":[[2021,2,8]],"date-time":"2021-02-08T00:00:00Z","timestamp":1612742400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/journals\/pages\/open_access\/funder_policies\/chorus\/standard_publication_model"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2021,7,7]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec><jats:title>Background<\/jats:title><jats:p>Hydroxychloroquine (HCQ) and methotrexate (MTX) are common antirheumatic drugs used chronically by patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) (1, 2). Therapeutic drug monitoring (TDM) of HCQ and MTX provides critical compliance information, but typically requires venipuncture and shipment of refrigerated blood samples to the clinical laboratory. Capillary blood collection by finger prick offers a convenient alternative to venipuncture. The long-term stability of capillary blood HCQ and MTX collected using volumetric absorptive microsamplers (VAMS) has not previously been evaluated. In this study, we evaluated the stability of capillary MTX and HCQ levels when stored on VAMS for up to 5\u2009years.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>Samples of patients with RA and SLE were collected for HCQ or MTX monitoring as part of 2 clinical studies in 2015 (HCQ: n\u2009=\u200924 | MTX: n\u2009=\u200961) and 2017 (HCQ: n\u2009=\u2009126). Venous and capillary blood samples were shipped to Exagen Inc.\u2019s clinical laboratory. HCQ and MTXPG3 were measured using separate LC-MS\/MS methodologies. Baseline venous blood levels of HCQ and MTXPG3 were determined within 1\u2009week of draw and compared to capillary blood levels determined following 3 or 5\u2009years of storage.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Venous blood HCQ and capillary blood MTXPG3 determinations made at baseline were significantly different from capillary blood determinations performed following 5\u2009years of storage at \u221280\u2009\u00b0C. However, these differences were within the specified limits of agreement [HCQ: Avg % change after storage (CI 95%)\u2009=\u2009\u22127.1% (\u221212.6, \u22121.6%), pt-test\u2009=\u20090.0205, interclass correlation coefficient (ICC)\u2009=\u20090.96 | MTXPG3: Avg % change after storage (CI 95%)\u2009=\u200913.3% (7.1, 19.4%), pt-test\u2009=\u20090.0001, ICC\u2009=\u20090.90].<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>Dried capillary blood HCQ and MTXPG3 levels collected on VAMS are stable for up to 5\u2009years.<\/jats:p><\/jats:sec>","DOI":"10.1093\/jalm\/jfaa221","type":"journal-article","created":{"date-parts":[[2020,11,30]],"date-time":"2020-11-30T20:15:58Z","timestamp":1606767358000},"page":"858-867","source":"Crossref","is-referenced-by-count":7,"title":["Capillary Blood Levels of Hydroxychloroquine and Methotrexate Are Stable for up to 5 Years When Collected on Volumetric Absorptive Microsamplers"],"prefix":"10.1093","volume":"6","author":[{"given":"Kelley","family":"Brady","sequence":"first","affiliation":[{"name":"Research and Development, Exagen Inc, 1261 Liberty Way, Suite C, Vista CA 92081"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Roberta Vezza","family":"Alexander","sequence":"additional","affiliation":[{"name":"Research and Development, Exagen Inc, 1261 Liberty Way, Suite C, Vista CA 92081"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Deborah","family":"Stimson","sequence":"additional","affiliation":[{"name":"Research and Development, Exagen Inc, 1261 Liberty Way, Suite C, Vista CA 92081"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mark","family":"Rudolph","sequence":"additional","affiliation":[{"name":"Research and Development, Exagen Inc, 1261 Liberty Way, Suite C, Vista CA 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