Direct and indirect reference intervals of 25-hydroxyvitamin D: it is not a real vitamin D deficiency pandemic

• Published in: Biochemia Medica Vol. 34; no. 2; p. 020706
• Main Authors: Perales-Afán, Juan José, Aparicio-Pelaz, Diego, López-Triguero, Sheila, Llorente, Elena, Puente-Lanzarote, Juan José, Fabre, Marta
• Format: Journal Article Paper
• Language: English
• Published: Croatia Medicinska naklada 15.06.2024; Croatian Society of Medical Biochemistry and Laboratory Medicine
• Subjects: Adolescent; Adult; Aged; Female; Humans; Immunoassay - standards; Male; Middle Aged; Original; Pandemics; Prospective Studies; Reference Values; Retrospective Studies; Seasons; Spain - epidemiology; Vitamin D - analogs & derivatives; Vitamin D - blood; Vitamin D Deficiency - blood; Vitamin D Deficiency - diagnosis; Vitamin D Deficiency - epidemiology; vitamin D, season, immunoassay; Young Adult; Spain; retrospective studies; prospective studies; vitamin D, season, immunoassay
• ISSN: 1330-0962; 1846-7482
• DOI: 10.11613/BM.2024.020706

Many 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. Two 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. Reference 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 < 0.001). Reference 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.