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. 2012 Jul;82(1):84-9.
doi: 10.1038/ki.2012.19. Epub 2012 Mar 7.

Bioavailable vitamin D is more tightly linked to mineral metabolism than total vitamin D in incident hemodialysis patients

Ishir Bhan  1 , Camille E Powe, Anders H Berg, Elizabeth Ankers, Julia B Wenger, S Ananth Karumanchi, Ravi I Thadhani
Affiliations

Bioavailable vitamin D is more tightly linked to mineral metabolism than total vitamin D in incident hemodialysis patients

Ishir Bhan et al. Kidney Int. 2012 Jul.

Abstract

Prior studies showed conflicting results regarding the association between 25-hydroxyvitamin D (25(OH)D) levels and mineral metabolism in end-stage renal disease. In order to determine whether the bioavailable vitamin D (that fraction not bound to vitamin D-binding protein) associates more strongly with measures of mineral metabolism than total levels, we identified 94 patients with previously measured 25(OH)D and 1,25-dihydroxyvitamin D (1,25(OH)(2)D) from a cohort of incident hemodialysis patients. Vitamin D-binding protein was measured from stored serum samples. Bioavailable 25(OH)D and 1,25(OH)(2)D were determined using previously validated formulae. Associations with demographic factors and measures of mineral metabolism were examined. When compared with whites, black patients had lower levels of total, but not bioavailable, 25(OH)D. Bioavailable, but not total, 25(OH)D and 1,25(OH)(2)D were each significantly correlated with serum calcium. In univariate and multivariate regression analysis, only bioavailable 25(OH)D was significantly associated with parathyroid hormone levels. Hence, bioavailable vitamin D levels are better correlated with measures of mineral metabolism than total levels in patients on hemodialysis.

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Conflict of interest statement

Disclosure

The authors have no competing financial interests to declare.

Figures

Figure 1
Figure 1
Total vs bioavailable 25(OH)D and serum calcium. Total levels of 25(OH)D demonstrated no association with serum calcium levels (corrected for albumin) while bioavailable 25(OH)D levels were positively associated with serum calcium.
Figure 2
Figure 2
Total vs bioavailable 25(OH)D and PTH. After adjustment for age, gender, race, and survival status at one year, bioavailable 25(OH)D was significantly negatively associated with PTH levels, while total 25(OH)D demonstrated no association with PTH.
Figure 3
Figure 3
Sample selection. 25(OH)D and 1,25(OH)2D were previously measured as part of a case-control study within the ArMORR cohort. Equal numbers of cases (subjects who died within their first year on dialysis) and controls were randomly selected from each racial group.
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