Prevalence of calcidiol deficiency in CKD: a cross-sectional study across latitudes in the United States.

Background: Recent Kidney Disease Outcomes Quality Initiative guidelines have raised concerns of 25-hydroxyvitamin D, or calcidiol, insufficiency and deficiency in patients with chronic kidney disease (CKD) not yet on dialysis therapy; however, no cross-sectional study across latitudes has been performed to support this assertion.
Methods: Baseline screening data from a prospective study were used to determine calcidiol levels in subjects with moderate to severe CKD not yet on dialysis therapy from 12 geographically diverse regions of the United States. Calcidiol deficiency is defined as levels less than 10 ng/mL (< 25 nmol/L), and insufficiency, as levels of 10 to 30 ng/mL (25 to 75 nmol/L).
Results: Two hundred one subjects with a mean age 65 +/- 13 years and calculated glomerular filtration rate (GFR) of 27 +/- 11 mL/min (0.45 mL/s) were evaluated. Overall mean calcidiol level was 19.4 +/- 13.6 ng/mL (48 +/- 34 nmol/L), with a range of 0 to 65 ng/mL (0 to 162 nmol/L). Only 29% and 17% of subjects with moderate and severe CKD had sufficient levels, respectively. Mean calcidiol levels were less than sufficient levels in all geographic locations tested. Multivariate analysis found log calcidiol level correlated with calcium level (P = 0.016), log calcitriol level (P = 0.024), sex (P = 0.041), geographic location (P = 0.045), and inverse intact parathyroid hormone level (P = 0.013), but not calculated GFR or phosphorous level. Calcidiol levels changed modestly in 18 patients who had calcidiol levels measured in winter and late summer after confirmed exposure to sunlight, with mean calcidiol levels of 17.9 +/- 11.7 to 21.2 +/- 10.0 ng/mL (45 +/- 29 to 53 +/- 25 nmol/L; P = 0.015).
Conclusion: This cross-sectional cohort study found a high prevalence of calcidiol deficiency and insufficiency in patients with moderate and severe CKD not on dialysis therapy regardless of geographic location.