{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,16]],"date-time":"2026-07-16T11:42:37Z","timestamp":1784202157276,"version":"3.55.0"},"reference-count":30,"publisher":"Croatian Society for Medical Biochemistry and Laboratory Medicine","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Biochem. med. (Online)"],"published-print":{"date-parts":[[2024,6,15]]},"abstract":"<jats:p>Graphical abstract\nHighlights\n\u2022 Addressing vitamin D deficiency, we established reference intervals using direct and indirect methods\n\u2022 Winter reference intervals (5.4-55.7 ng\/mL) contrasts with higher summer values (5.9-59.9 ng\/mL), emphasizing the impact of seasons\n\u2022 Differences between vitamin D reference intervals obtained by direct and indirect methods were detected\n\u2022 The importance of regional factors is critical; notable distinctions in vitamin D values underscore the need for revised guidelines\nIntroductionMany studies report vitamin D (25-OH-D) deficiency, although there is no consensus among scientific societies on cut-offs and reference intervals (RI). The aim of this study is to establish and compare RI for serum 25-OH-D by direct and indirect methods.\nMaterials and methodsTwo studies were performed in Zaragoza (Spain). A retrospective study (N = 7222) between January 2017 and April 2019 was used for RI calculation by indirect method and a prospective study (N = 312) with healthy volunteers recruited in August 2019 and February 2020 for direct method. Seasonal differences were investigated. Measurements were performed on Cobas C8000 (Roche-Diagnostics, Basel, Switzerland) using electrochemiluminescence immunoassay technology.\nResultsReference intervals (2.5-97.5 percentile and corresponding 95% confidence intervals, CIs) were as follows: by indirect method 5.6 ng\/mL (5.4 to 5.8) - 57.2 ng\/mL (55.2 to 59.8), in winter 5.4 ng\/mL (5.2 to 5.7) - 55.7 ng\/mL (53.6 to 58.4), while in summer 5.9 ng\/mL (5.4 to 6.2) - 59.9 ng\/mL (56.3 to 62.9). By direct method 9.0 ng\/mL (5.7 to 9.5) - 41.4 ng\/mL (37.6 to 48.0), in winter 7.4 ng\/mL (3.9 to 8.6) - 34.6 ng\/mL (30.6 to 51.5), while in summer 13.3 ng\/mL (10.1 to 14.1) - 44.1 ng\/mL (38.9 to 66.0). In both methods, RIs were higher in summer. A significant difference was observed in 25-OH-D median values between the two methods (P &lt; 0.001).\nConclusionsReference interval calculation according to the studied area may be a useful tool to adapt the deficiency cut-offs for 25-OH-D. Our data support 25-OH-D values over 12.0 ng\/mL for healthy population as sufficient, therefore current recommendations should be updated. In addition, differences in seasonality should be taken into account.<\/jats:p>","DOI":"10.11613\/bm.2024.020706","type":"journal-article","created":{"date-parts":[[2024,6,12]],"date-time":"2024-06-12T08:39:21Z","timestamp":1718181561000},"page":"295-302","source":"Crossref","is-referenced-by-count":2,"title":["Direct and indirect reference intervals of 25-hydroxyvitamin D"],"prefix":"10.11613","volume":"34","author":[{"given":"Marta","family":"Fabre","sequence":"first","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juan Jos\u00e9","family":"Puente-Lanzarote","sequence":"additional","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elena","family":"Llorente","sequence":"additional","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sheila","family":"L\u00f3pez-Triguero","sequence":"additional","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Diego","family":"Aparicio-Pelaz","sequence":"additional","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Juan Jos\u00e9","family":"Perales-Af\u00e1n","sequence":"additional","affiliation":[{"name":"Clinical Biochemistry Department, Lozano Blesa University Hospital, Zaragoza, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"4885","published-online":{"date-parts":[[2024,6,15]]},"reference":[{"key":"key20240612043918_r1","doi-asserted-by":"crossref","first-page":"858","DOI":"10.3945\/jn.116.244079","article-title":"Ambient UVB Dose and Sun Enjoyment Are Important Predictors of Vitamin D Status in an Older Population.","volume":"147","author":"O\u2019Sullivan","year":"2017","journal-title":"J Nutr"},{"key":"key20240612043918_r2","doi-asserted-by":"crossref","first-page":"755","DOI":"10.1093\/ajcn\/45.4.755","article-title":"Vitamin D status in the elderly: seasonal substrate deficiency causes 1,25-dihydroxycholecalciferol deficiency.","volume":"45","author":"Bouillon","year":"1987","journal-title":"Am J Clin Nutr"},{"key":"key20240612043918_r3","doi-asserted-by":"crossref","first-page":"V28","DOI":"10.1359\/jbmr.07s211","article-title":"Vitamin D and skin physiology: a D-lightful story.","volume":"22","author":"Holick","year":"2007","journal-title":"J Bone Miner Res"},{"key":"key20240612043918_r4","doi-asserted-by":"crossref","DOI":"10.1136\/bmjopen-2018-024797","article-title":"Changes to the frequency and appropriateness of vitamin D testing after the introduction of new Medicare criteria for rebates in Australian general practice: evidence from 1.5 million patients in the NPS Medicine Insight database.","volume":"9","author":"Gonzalez-Chica","year":"2019","journal-title":"BMJ Open"},{"key":"key20240612043918_r5","doi-asserted-by":"crossref","DOI":"10.11613\/BM.2020.020501","article-title":"In sickness and in health: pivotal role of vitamin D.","volume":"30","author":"Nikolac Gabaj","year":"2020","journal-title":"Biochem Med (Zagreb)"},{"key":"key20240612043918_r6","doi-asserted-by":"crossref","first-page":"520","DOI":"10.1056\/NEJMoa1900906","article-title":"Vitamin D Supplementation and Prevention of Type 2 Diabetes.","volume":"381","author":"Pittas","year":"2019","journal-title":"N Engl J Med"},{"key":"key20240612043918_r7","doi-asserted-by":"crossref","first-page":"996","DOI":"10.3390\/jpm13060996","article-title":"The Effects of Vitamin D Supplementation before 20 Weeks of Gestation on Preeclampsia: A Systematic Review.","volume":"13","author":"Dahma","year":"2023","journal-title":"J Pers Med"},{"key":"key20240612043918_r8","doi-asserted-by":"crossref","first-page":"1823","DOI":"10.1186\/s12889-021-11888-1","article-title":"MeshbahurRahman M. 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