{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,15]],"date-time":"2026-04-15T15:11:30Z","timestamp":1776265890983,"version":"3.50.1"},"reference-count":25,"publisher":"Centre for Evaluation in Education and Science (CEON\/CEES)","issue":"4","license":[{"start":{"date-parts":[[2026,1,1]],"date-time":"2026-01-01T00:00:00Z","timestamp":1767225600000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/BY\/4.0"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J Med Biochemistry"],"published-print":{"date-parts":[[2026]]},"abstract":"<jats:p>Background: The timing of sample collection is crucial for analytes with a circadian rhythm. Although blood samples are usually collected in the morning, they can also be collected in the afternoon. Our study aims to evaluate the impact of sampling time on Thyroid-Stimulating Hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3). Methods: Serum TSH, fT4, and fT3 measurements from 216,278 patients who visited our institute's outpatient clinics over two years (2021-2023) were obtained from laboratory data. After exclusions, 5,953 patient results collected from 8 am to 5 pm were grouped into 1-hour intervals. All measurements were performed using the Cobas e801 (Roche Diagnostics, Penzberg, Germany) with the electrochemiluminescence immunoassay method. Statistical significance was tested with the standard normal deviation test (Z-test), and clinical significance was assessed using bias % values obtained from biologic variation estimates on the website of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM). Results: Each TSH hourly group between 11 am and 5 pm showed statistically and clinically significant differences compared to the reference group. No statistically significant differences were observed for either fT4 or fT3. However, fT4 levels showed a clinically significant difference at a single time point in males, while fT3 levels showed clinically significant differences between 3-5 pm in females and 2-5 pm in males. Conclusion: Our analysis of an extensive dataset indicates that the timing of blood sampling significantly affects TSH results. This may cause misinterpretation in clinical settings if standardization is not provided.<\/jats:p>","DOI":"10.5937\/jomb0-61454","type":"journal-article","created":{"date-parts":[[2026,2,19]],"date-time":"2026-02-19T08:18:32Z","timestamp":1771489112000},"page":"897-906","source":"Crossref","is-referenced-by-count":0,"title":["Significance of sampling time on thyroid-stimulating hormone, free thyroxine, and free triiodothyronine levels"],"prefix":"10.5937","volume":"45","author":[{"suffix":"Mert","given":"Mahmut","family":"Daglar","sequence":"first","affiliation":[{"name":"Dr. Lutfi Kirdar City Hospital, Department of Biochemistry Laboratory, Istanbul, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Asuman","family":"Or\u00e7un","sequence":"additional","affiliation":[{"name":"Dr. Lutfi Kirdar City Hospital, Department of Biochemistry Laboratory, Istanbul, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"3964","reference":[{"key":"ref1","doi-asserted-by":"crossref","unstructured":"Andersen S, Bruun NH, Pedersen KM, Laurberg R Biologic variation is important for interpretation of thyroid function tests. 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