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Osteoporos Int. 2017 Aug;28(8):2457-2464. doi: 10.1007/s00198-017-4062-8. Epub 2017 May 2.

Comparison of total, free and bioavailable 25-OH vitamin D determinations to evaluate its biological activity in healthy adults: the LabOscat study.

Author information

1
Hospital Clínic de Barcelona, IDIBAPS. CIBERehd, Barcelona, Spain. pperis@clinic.ub.es.
2
Servicio de Bioquímica Clínica, Hospital Clinic, Barcelona, Spain.
3
Hospital Clínic de Barcelona, IDIBAPS. CIBERehd, Barcelona, Spain.
4
Hospital de l'Alt Penedés, Barcelona, Spain.
5
Hospital Arnau de Vilanova, Lleida, Spain.
6
Instituto Universitario Parc Taulí, Barcelona, Spain.
7
Hospital Moisés Broggi, Barcelona, Spain.
8
Hospital Universitari de Bellvitge, Barcelona, Spain. aerra@hsrafael.es.
9
Hospital San Rafael, Madrid, Spain.
10
Hospital Mútua de Terrassa, Madrid, Spain.
11
Hospital Sta María, Barcelona, Spain.
12
Hospital Esperit Sant, Barcelona, Spain.
13
Hospital de Vic, Barcelona, Spain.
14
Hospital de Figueres, Barcelona, Spain.
15
Hospital de Ganollers, Catalonia, Spain.
16
Departament de Fonaments Clínics, Universitat de Barcelona, Barcelona, Spain.

Abstract

Determination of different forms of 25-OHD (total, free and bioavailable) in healthy young women does not offer additional advantages over standard 25-OHDT for evaluating vitamin D deficiency. In these subjects 25-OHDT values <15 ng/ml would be more appropriate for defining this deficiency.

INTRODUCTION:

Determination of 25-OH vitamin D serum levels (25-OHD) constitutes the method of choice for evaluating vitamin D deficiency. However, vitamin D-binding protein (DBP) may modulate its bioavailability thereby affecting correct evaluation of 25-OHD status. We analysed the impact of the determination of 25-OHD (total, free and bioavailable) on the evaluation its biologic activity (estimated by serum PTH determination) in healthy young women.

METHODS:

173 premenopausal women (aged 35-45 yrs.) were included. We analysed serum values of total 25-OHD (25-OHDT), DBP, albumin, PTH and bone formation (PINP,OC) and resorption (NTx,CTx) markers. Free(25-OHDF) and bioavailable (25-OHDB) serum 25-OHD levels were estimated by DBP and albumin determinations and also directly by ELISA (25-OHDF-2). We analysed threshold PTH values for the different forms of 25-OHD and the correlations and differences according to 25-OHDT levels <20 ng/ml.

RESULTS:

62% of subjects had 25-OHD values <20 ng/ml and also had significantly lower 25-OHDF and 25-OHDB values, with no significant differences in bone markers and PTH values. The PTH threshold value was similar for all forms of 25-OHD (∼70 pg/ml). Women with PTH values >70 had lower 25-OHDT (15.4 ± 1.4 vs. 18.3 ± 2.7, p < 0.05) and 25OHDB values (1.7 ± 0.2 vs. 2.2 ± 0.09, p < 0.05). The different forms of 25OHD were significantly intercorrelated, with marginal correlations between PTH and 25-OHDT (r = -0.136, p = 0.082).

CONCLUSIONS:

Determination of different forms of 25-OHD in healthy young women does not offer additional advantages over standard 25-OHDT for evaluating vitamin D deficiency. In these subjects 25-OHDT values <15 ng/ml would be more appropriate for defining this deficiency.

KEYWORDS:

25-Hydroxyvitamin D; Bioavailable vitamin D; DBP; Free vitamin D; Vitamin D deficiency; Vitamin D insufficiency

PMID:
28466136
DOI:
10.1007/s00198-017-4062-8
[Indexed for MEDLINE]

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