{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T19:01:35Z","timestamp":1790276495956,"version":"4.1.0"},"reference-count":20,"publisher":"Wiley","issue":"2","license":[{"start":{"date-parts":[[2022,10,31]],"date-time":"2022-10-31T00:00:00Z","timestamp":1667174400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Clinical Endocrinology"],"published-print":{"date-parts":[[2023,8]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec><jats:title>Objective<\/jats:title><jats:p>To investigate the effect of CRYSVITA\u00ae (burosumab\u2010twza) on FGF23 measurements in an intact and a C\u2010terminal immunoassay.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>An intact serum FGF23 (MedFrontier) and a C\u2010terminal plasma FGF23 assay (Immutopics) were used. Serum\/plasma pools were spiked to span the burosumab therapeutic range (1.4\u201311.3\u2009\u03bcg\/ml) and FGF23 recovery was assessed. Patient serum and plasma samples obtained pre and post\u2010burosumab treatment were evaluated on both assays and compared with corresponding phosphorus measurements<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Spiking burosumab (1.4\u201311.3\u2009\u03bcg\/ml) into sample pools resulted in a dose\u2010dependent negative analytical interference on intact FGF23 measurements and no significant interference for C\u2010terminal FGF23 measurements. However, more than a 500\u2010fold median increase (post\u2010 vs. pre\u2010burosumab administration) in in vivo FGF23 concentrations were observed by both assays.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>Therapeutic concentrations of burosumab result in a negative analytical interference of the intact, but not the C\u2010terminal FGF23 immunoassay. Despite this in vitro analytical interference in the intact assay, relatively large elevations of both intact FGF23 and C\u2010terminal FGF23 measurements were observed in vivo following burosumab administration. Following burosumab administration, FGF23 measurements must be interpreted within the clinical context of the patient and other relevant biomarker results.<\/jats:p><\/jats:sec><jats:sec><jats:title>Summary<\/jats:title><jats:p>This article describes a negative analytical interference by burosumab in an intact FGF23 immunoassay. The recovery of C\u2010terminal FGF23 is not significantly affected by the presence of burosumab. In vivo, both assays demonstrate extreme FGF23 elevations in the presence of the drug. Furthermore, the measurement of FGF23 blocked by burosumab is not clinically useful regarding hypophosphataemia.<\/jats:p><\/jats:sec>","DOI":"10.1111\/cen.14832","type":"journal-article","created":{"date-parts":[[2022,10,20]],"date-time":"2022-10-20T07:28:52Z","timestamp":1666250932000},"page":"152-157","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["The effect of burosumab on intact and C\u2010terminal FGF23 measurements"],"prefix":"10.1111","volume":"99","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2991-129X","authenticated-orcid":false,"given":"Susan Louise","family":"Ashrafzadeh\u2010Kian","sequence":"first","affiliation":[{"name":"Department of Laboratory Medicine and Pathology Mayo Clinic  Minnesota Rochester USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nobuaki","family":"Ito","sequence":"additional","affiliation":[{"name":"Division of Nephrology and Endocrinology The University of Tokyo Hospital Tokyo Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8654-0627","authenticated-orcid":false,"given":"Tarak","family":"Srivastava","sequence":"additional","affiliation":[{"name":"Department of Pediatrics, Section of Nephrology Children's Mercy Hospital  Missouri Kansas City USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Uttam","family":"Garg","sequence":"additional","affiliation":[{"name":"Department of Pathology &amp; Laboratory Medicine Children's Mercy Hospital  Kansas City Missouri USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9178-7846","authenticated-orcid":false,"given":"Hajime","family":"Kato","sequence":"additional","affiliation":[{"name":"Division of Nephrology and Endocrinology The University of Tokyo Hospital Tokyo Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alicia","family":"Algeciras\u2010Schimnich","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine and Pathology Mayo Clinic  Minnesota Rochester USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Joshua A.","family":"Bornhorst","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine and Pathology Mayo Clinic  Minnesota Rochester USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2022,10,31]]},"reference":[{"key":"e_1_2_9_2_1","doi-asserted-by":"publisher","DOI":"10.1007\/s40267-018-0560-9"},{"key":"e_1_2_9_3_1","doi-asserted-by":"publisher","DOI":"10.3389\/fendo.2018.00189"},{"key":"e_1_2_9_4_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.clinbiochem.2019.03.002"},{"key":"e_1_2_9_5_1","doi-asserted-by":"publisher","DOI":"10.1002\/jbmr.4620"},{"key":"e_1_2_9_6_1","doi-asserted-by":"publisher","DOI":"10.1507\/endocrj.EJ21-0386"},{"key":"e_1_2_9_7_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00223-020-00659-6"},{"key":"e_1_2_9_8_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.berh.2011.10.020"},{"key":"e_1_2_9_9_1","doi-asserted-by":"publisher","DOI":"10.1038\/ki.2012.176"},{"key":"e_1_2_9_10_1","doi-asserted-by":"publisher","DOI":"10.1210\/jc.2006-2865"},{"key":"e_1_2_9_11_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00774-005-0625-4"},{"key":"e_1_2_9_12_1","doi-asserted-by":"publisher","DOI":"10.1210\/jc.2005-2105"},{"key":"e_1_2_9_13_1","unstructured":"MedFrontier FGF23Intact Product Flyer. 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