Archief Roodbont

March 4, 2010 — Vitamin D deficiency is almost universal in patients with kidney disease with low blood albumin levels who begin long-term dialysis during the winter, according to the results of a study reported in the March issue of the Clinical Journal of the American Society of Nephrology.

"This research identifies risk factors for nutritional vitamin D deficiency in the dialysis population and may provide clues to its biology in this population," lead author Ishir Bhan, MD, MPH, from Massachusetts General Hospital in Boston, said in a news release.

The goal of this study was to examine whether routinely measured clinical and demographic factors could identify patients starting dialysis who are deficient in vitamin D. The study cohort, which was divided into training (60%) and validation (40%) sets, consisted of 908 patients with 25-hydroxyvitamin D levels who were enrolled in the Accelerated Mortality on Renal Replacement (ArMORR) cohort of incident US patients initiating dialysis.

Using logistic regression modeling, neural networks, and decision trees with vitamin D deficiency as the dependent variable, the investigators generated predictive models from routinely determined clinical and demographic data in the training set. To identify the simplest model that remained predictive, the investigators subjected the models to progressive variable reduction.

Vitamin D deficiency, defined as 25-hydroxyvitamin D levels of less than 30 ng/mL, was present in 79% of the study population. The strongest predictors of vitamin D deficiency were black race, female sex, winter season, and hypoalbuminemia (serum albumin levels ≤ 3.1 g/dL). In the validation set, factors of hypoalbuminemia and dialysis started during the winter season increased the likelihood of vitamin D deficiency from 90% to 100% in black women, from 85% to 100% in black men, from 82% to 94% in white women, and from 66% to 92% in white men.

"Deficiency of 25-hydroxyvitamin D is nearly universal among patients with hypoalbuminemia initiating chronic hemodialysis in winter," the study authors write.

Limitations of this study include lack of generalizability to non-US populations, uncertain direction of causality, and possible residual confounding. In addition, further studies are needed to determine if repleting 25-hydroxyvitamin D levels affect hyperglycemia, blood pressure, infection rates, or mortality rates in end-stage renal disease (ESRD).

"Although this study identified clinical factors that predicted low 25-hydroxyvitamin D levels, it is not yet proven that correcting these levels is clinically beneficial," the study authors conclude. "Prospective studies in ESRD, some of which are now underway, are needed to identify optimal levels of 25-hydroxyvitamin D for a range of functions and to further elucidate its biology. In the absence of clinical trials, clinicians must independently determine if these findings should guide empiric therapy or simply inform future studies."

Some of the study authors have disclosed various financial relationships with the National Kidney Foundation, the National Institutes of Health, and/or Abbott Laboratories.

Clin J Am Soc Nephrol. 2010;5:460-467.