Low 25-Hydroxyvitamin D Levels and Mortality in Non-Dialysis-Dependent CKD

Background: Low 25-hydroxyvitamin D (25[OH]D) levels are common in patients with non-dialysis-dependent chronic kidney disease (CKD). The associations between low 25(OH)D levels and mortality in non-dialysis-dependent patients with CKD are unclear. Study Design: Retrospective cohort study. Setting & Participants: Patients with stages 3-4 CKD (estimated glomerular filtration rate, 15-59 mL/min/1.73 m(2); n = 12,673) who had 25(OH)D levels measured after the diagnosis of CKD in the Cleveland Clinic Health System. Predictor: 25(OH)D levels categorized into 3 groups: <15, 15-29, and >= 30 ng/mL. Outcomes: We examined factors associated with low 25(OH) D levels and associations between low 25(OH)D levels and all-cause mortality (ascertained using the Social Security Death Index and our electronic medical record) using logistic regression, Cox proportional hazard models, and Kaplan-Meier survival curves. Measurements: 25(OH)D was measured using chemiluminescence immunoassay. Results: Of 12,763 patients with CKD, 15% (n = 1,970) had 25(OH) D levels <15 ng/mL, whereas 45% (n = 5,749) had 25(OH)D levels of 15-29 ng/mL. Male sex, African American race, diabetes, coronary artery disease, and lower estimated glomerular filtration rate were associated significantly with 25(OH)D level <30 ng/mL. A graded increase in risk of 25(OH)D level <30 ng/mL was evident across increasing body mass index levels. Patients who had 25(OH)D levels measured in fall through spring had higher odds for 25(OH)D levels <30 ng/mL. After covariate adjustment, patients with CKD with 25(OH)D levels <15 ng/mL had a 33% increased risk of mortality (95% CI, 1.07-1.65). The group with 25(OH)D levels of 15-29 ng/mL did not show a significantly increased risk of mortality (HR, 1.03; 95% CI, 0.86-1.22) compared with patients with 25(OH)D levels >= 30 ng/mL. Limitations: Single-center observational study, lack of data for albuminuria and other markers of bone and mineral disorders, and attrition bias. Conclusions: 25(OH)D level <15 ng/mL was associated independently with all-cause mortality in non-dialysis-dependent patients with CKD. Am J Kidney Dis. 58(4): 536-543. (C) 2011 by the National Kidney Foundation, Inc.