In:
Clinical Chemistry, Oxford University Press (OUP), Vol. 52, No. 2 ( 2006-02-01), p. 248-254
Abstract:
Background: Clinical assessment of vitamin D status often relies on measuring total circulating 25-hydroxyvitamin D3 (25OHD3), but much of each vitamin D metabolite is bound to plasma vitamin D–binding protein (DBP), such that the percentage of free vitamin is very low. We hypothesized that measurement of free rather than total 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 25OHD3 may provide better assessment of vitamin D status. We therefore aimed to assess vitamin D status in men with idiopathic osteoporosis, in whom possible secondary causes of osteoporosis had been excluded, and to determine the extent of change in biologically active “free” vitamin D caused by variation in plasma DBP concentrations. Methods: We measured 1,25(OH)2D3 and 25OHD3 in plasma samples from 56 men with idiopathic osteoporosis [mean (SD) age, 59.6 (13.6) years; range, 21–86 years] and 114 male controls [62.4 (10.4) years; range, 44–82 years] . Results: Mean total plasma 25OHD3 in the 56 men with osteoporosis and the 114 controls was 44.7 (21) and 43.3 (17) nmol/L, respectively; total plasma 1,25(OH)2D3 measured in randomly selected men with osteoporosis (n = 50) and controls (n = 50) was 90 (37) and 103 (39) pmol/L, respectively. Mean plasma DBP was significantly higher (P & lt;0.001) in men with osteoporosis [224 (62) mg/L; n = 56] than in the controls [143 (34) mg/L; n = 114] , but calculated free plasma 25OHD3 and 1,25(OH)2D3 were significantly lower in the osteoporotic men than in controls [6.1 (3.1) vs 9.1 (4.4) pmol/L (P & lt;0.00001) and 77 (37) vs 142 (58) fmol/L (P & lt;0.00001), respectively]. Conclusions: Measurement of total vitamin D metabolites alone, although providing a crude assessment of vitamin D status, may not give an accurate indication of the free (biologically active) form of the vitamin. The ratio of total 25OHD3 and 1,25(OH)2D3 to plasma DBP, rather than total circulating vitamin D metabolites, may provide a more useful index of biological activity. Further studies are required to substantiate this hypothesis.
Type of Medium:
Online Resource
ISSN:
0009-9147
,
1530-8561
DOI:
10.1373/clinchem.2005.059568
Language:
English
Publisher:
Oxford University Press (OUP)
Publication Date:
2006
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