25‐Hydroxy Vitamin D Levels in Hemodialysis‐Requiring End‐Stage Renal Disease Patients

BACKGROUND Low vitamin D serum levels represent an additional risk factor for end-stage renal disease (ESRD)–associated bone disorders. The aim of this study was to evaluate the prevalence of vitamin D deficiency in both the summer and winter seasons, as well as to define the associated risk factors, and to establish the link between secondary hyperparathyroidism and circulating 25-hydroxy vitamin D (25 [OH]-D) serum levels. METHODS Seventy-eight hemodialysis (HD)–requiring ESRD outpatients living in Buenos Aires, Argentina, age 57.2 ± 2.07 years (21–86 years) were evaluated at the end of summer (SUM) and the end of winter (WIN). Then 25 (OH)-D, serum calcium (Ca), intact parathormone, ionized Ca (Ca11), phosphate, alkaline phosphatase, creatinine, C-reactive protein, and serum albumin were evaluated. The participants were evaluated according to the 25 (OH)-D levels following KDOQI guidelines. The participants were assigned to 2 groups according to their Karnofsky scores for functional capacity (FC): FC 1–2 (normal physical capacity full-time to only part-time) and FC 3–4 (limited capacity only for self care to needs permanent assistance). RESULTS Seasonal variations in 25 (OH)-D (WIN 18.1 ± 1.15 ng/mL vs. SUM 29.2 ± 1.35 ng/mL, p < 0.001) were verified. Male patients displayed higher 25 (OH)-D serum levels than female participants (20.3 ± 1.5 ng/mL vs. 15.4 ± 1.6 ng/mL, p < 0.01). We observed (WIN/SUM) vitamin D deficiency in 48.7/11.8%, insufficiency in 41/39.5%, and target levels in 10.3/48.7% of the population. Severe deficiency was not detected. The mean variation in WIN/SUM 25 (OH)-D level was 11.08 ± 1.04 ng/mL, which correlated with age (r = 20.59, p = 0.02). Patients with FC 3–4 displayed the lowest 25 (OH)-D levels, and this was associated with older age (70.8 ± 3.12 years vs. 50.4 ± 2.16 years, p < 0.01), severe disease (C-reactive protein: 22.8 ± 6.26 mg/L vs. 10.2 ± 2.8 mg/L, p = 0.02), and poor nutritional status (albumin: 3.8 ± 0.09 vs. 4.1 ± 0.04, p = 0.0049; creatinine: 7.4 ± 0.4 mg/dL vs. 8.4 ± 0.29 mg/dL, p = 0.04). Multivariate analysis with 25 (OH)-D as the dependent variable demonstrated that both FC and sex independently predicted serum levels of 25 (OH)-D. No association between intact parathormone and 25 (OH)-D was detected. CONCLUSIONS Fifty percent of the HD-requiring ESRD patients showed 25 (OH)-D insufficiency/deficiency. This finding was more frequent in winter. Women and older patients were at higher risk. Those individuals displaying optimal 25 (OH)-D levels showed better health indicators for HD-requiring ESRD patients. FC assessed through the Karnofsky score was a useful clinical parameter able to identify patients at risk of 25 (OH)-D deficiency. In our population, renal disease-associated secondary hyperparathyroidism did not correlate with vitamin D deficiency.