{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,16]],"date-time":"2026-08-16T16:35:21Z","timestamp":1786898121361,"version":"build-2736575974"},"reference-count":15,"publisher":"Walter de Gruyter GmbH","license":[{"start":{"date-parts":[[2026,8,17]],"date-time":"2026-08-17T00:00:00Z","timestamp":1786924800000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec id=\"j_cclm-2026-0410_abs_001\">\n                    <jats:title>Objectives<\/jats:title>\n                    <jats:p>24 hour urine free cortisol measurement is widely used for screening Cushing\u2019s syndrome, but its reliability is limited by variability due to inherent biological variation and variation introduced by collection errors. This study aimed to determine the proportion of inaccurately collected samples and evaluate the impact on urine free cortisol variability.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec id=\"j_cclm-2026-0410_abs_002\">\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>A retrospective analysis was conducted using paired 24-h urine samples from subjects screened for hypercortisolism at two academic hospitals in the Netherlands. Paired 24-h urine samples from 552 subjects were evaluated. Collection accuracy was determined by comparing creatinine and urine volume differences between consecutive samples. Samples were classified as inaccurate if the creatinine difference exceeded 4\u00a0mmol\/24\u202fh or the volume difference exceeded 55\u202f%.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec id=\"j_cclm-2026-0410_abs_003\">\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>19\u202f% of paired urine collections were classified as inaccurate. Accurate collections showed lower variability in urine free cortisol concentrations (coefficient of variation 17\u202f%) compared to inaccurate collections (coefficient of variation 33\u202f%).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec id=\"j_cclm-2026-0410_abs_004\">\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>This study shows that many routine 24-h urine samples are collected incorrectly. Collection errors contribute considerably to the total variability of 24-h urine free cortisol measurements. This highlights the importance of patient instruction and adherence to collection protocols for reproducibility of urine free cortisol measurements.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1515\/cclm-2026-0410","type":"journal-article","created":{"date-parts":[[2026,8,16]],"date-time":"2026-08-16T16:10:56Z","timestamp":1786896656000},"source":"Crossref","is-referenced-by-count":0,"title":["Evaluating variability in 24-hour urine free cortisol measurements: impact of sample collection errors"],"prefix":"10.1515","author":[{"given":"\u00d6mer","family":"\u00d6zcan","sequence":"first","affiliation":[{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, Vrije Universiteit Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-8363-5046","authenticated-orcid":false,"given":"Karlijn","family":"Koops","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, Vrije Universiteit Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jacquelien J.","family":"Hillebrand","sequence":"additional","affiliation":[{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Antonius E.","family":"van Herwaarden","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine , Radboud University Medical Center , Nijmegen , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Annenienke","family":"van de Ven","sequence":"additional","affiliation":[{"name":"Department Internal Medicine, Division of Endocrinology , Radboud University Medical Center , Nijmegen , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter H.","family":"Bisschop","sequence":"additional","affiliation":[{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Department of Endocrinology and Metabolism , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Movement Sciences , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wendy P.J.","family":"den Elzen","sequence":"additional","affiliation":[{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Laboratory Specialized Diagnostics & Research, Department of Laboratory Medicine , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Public Health , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Annemieke C.","family":"Heijboer","sequence":"additional","affiliation":[{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, Vrije Universiteit Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Gastroenterology, Endocrinology & Metabolism , Amsterdam , the Netherlands"},{"name":"Department of Laboratory Medicine, Endocrine Laboratory , Amsterdam UMC, University of Amsterdam , Amsterdam , the Netherlands"},{"name":"Amsterdam Reproduction & Development Research Institute , Amsterdam , the Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"374","published-online":{"date-parts":[[2026,8,17]]},"reference":[{"key":"2026081615563008262_j_cclm-2026-0410_ref_001","doi-asserted-by":"crossref","unstructured":"Guo, K, Zhao, X, Luo, J, Ren, Y, Liu, Y, Yang, J. 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