903 SERUM 24,25 DIHYDROXYVITAMIN D (24,25(0H)₂D) LEVELS IN UREMIA: A REFLECTION OF RENAL INSUFFICIENCY

Abstract

Serum concentrations of 24,25(OH)₂D, a metabolite of Vitamin D synthesized mainly by renal 25OHD-24 hydroxylase, and of 25OHD were measured in normal and uremic subjects by competitive protein binding radioassay after isolation by Sephadex LH-20 chromatography. The mean (±SE) concentration of 24,25(OH)₂D in 10 hemodialyzed children (H) (creatinine clearance(CrCl) < 5ml/min/1.73m²) was significantly (p < 01) lower (.87±.13ng/ml) than in 12 normal children (2.98±.45). Mean serum 24,25(OH)₂D in 10 azotemic children not requiring hemodialysis (CrCl>5-100) was also lower (1.30±.12, p < 01) than in normal children, but higher (p < 05) than in H. Mean radioassayable 25OHD concentrations were similar in all groups. Serum 24,25(OH)₂D levels and 24,25(OH)₂D/25OHD ratios correlated significantly with CrCl (r= .62, p < .01 and r=.76, p < 01, respectively) when all subjects were analyzed. In a group of 6 anephric adults, serum 24,25(OH)₂D levels (.55±.20) were lower (p < 01) than in 18 normal adults (1.70±.15) and undetectable in 3.

Conclusions: (1) Compromised renal function is associated with decreased serum 24,25(OH)₂D, an easily measured vitamin D metabolite; (2) 25OHD levels do not differ from normal in patients with renal insuffiency; 3) Diminished 24,25(OH)₂D values may parallel renal 1-hydroxylase activity which is also decreased in uremia; (4) Lowered 1,25(OH)₂D and 24,25(OH)₂D production may both contribute to the development of renal osteodystrophy.

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