Serum levels of 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, and 25-hydroxyvitamin D in nondialyzed patients with chronic renal failure

Background. In patients with chronic renal failure (CRF), abnormalities in vitamin D metabolism are known to be present, and several factors could con tribute to the abnormalities. Methods. We measured serum levels of three vitamin D metabolites, 1,25(OH)( 2)D, 24,25(OH)(2)D and 25(OH)D, and analyzed factors affecting their levels in 76 nondialyzed patients with CRF (serum creatinine > 1.6 and < 9.0 mg/d l), 37 of whom had diabetes mellitus (DM-CRF) and 39 of whom were nondiabet ic (nonDM-CRF). Results. Serum levels of 1,25(OH)(2)D were positively correlated with estim ated creatinine clearance (C-Cr; r = 0.429; P < 0.0001), and levels of 24,2 5(OH)(2)D were weakly correlated with C-Cr (r = 0.252, P < 0.05); no correl ation was noted for 25(OH)D. Serum levels of all three vitamin D metabolite s were significantly and positively correlated with serum albumin. Although there were no significant differences in age, sex, estimated C-Cr, calcium acid phosphate between DM-CRF and nonDM-CRF, all three vitamin D metabolit es were significantly lower in DM-CRF than in nonDM-CRF. To analyze factors influencing vitamin D metabolite levels, we performed multiple regression analyses. Serum 25(OH)D levels were significantly and independently associa ted with serum albumin, presence of DM and serum phosphate (R-2 = 0.599; P < 0.0001). 24,25(OH)(2)D levels were significantly and strongly associated with 25(OH)D (beta = 0.772; R-2 = 0.446; P < 0.0001). Serum 1,25(OH)(2)D le vels were significantly associated only with estimated C-Cr (R-2 = 0.409; P < 0.0001). Conclusions. These results suggest that hypoalbuminemia and the presence of DM independently affect serum 25(OH)D levels, probably via diabetic nephro pathy and poor nutritional status associated with diabetes, and that 25(OH) D is actively catalyzed to 24,25(OH)(2)D in CRF, probably largely via extra renal 24-hydroxylase. Serum levels of 1,25(OH)(2)D were significantly affec ted by the degree of renal failure. Thus, this study indicates that patient s with CRF, particularly those with DM, should receive supplements containi ng the active form of vitamin D prior to dialysis.