Vitamin D3 Metabolites in Chronic Renal Failure and After Renal Transplantation

Circulating vitamin D3 metabolites were measured in 31 adultpatients with chronic renal failure and 31 adults between 3and 30 months after renal transplantation. No subject excretedover 1 g urinary protein daily nor received vitamin D or itsmetabolites. There was a positive correlation between 1,25(OH)₂D3and GFR between 15 and 90 ml/min in both chronic renal failure(r=0.60, P<0.001) and transplant subjects (r=0.49, P<0.01)and between 1.25(OH)₂ and 25(OH)D3 after transplant (r=0.69,P<0.001), but not in chronic renal failure (r=0.22, P=ns).There was a weak inverse correlation between 1,25(OH)₂D3 andserum phosphate in chronic renal failure (r=0.36, P<0.05)but not post transplant (r=0.03, P=ns). Compared with 1,25(OH)₂D3concentrations in 16 normal subjects (mean±SEM: 39.5±1.9 pg/ml), chronic renal failure subjects with mild renal impairment(GFR 45–90 ml/min, mean: 61.5±3.3 ml/min, n=17)had reduced 1,25(OH)₂D3 (28.9±2.7 pg/ml, P<0.01).In transplant subjects with mild impairment (GFR 45–90ml/min, mean: 61.4±3.7), 1,25(OH)₂D3 was positively (r=0.79,P<0.001) and iPTH inversely correlated (r=0.51, P<0.05)with 25(OH)D3. In each of nine such subjects studied, seasonalvariations in 1,25(OH)₂ (P<0.001) and PTH (P<0.05, 1-tailedtest), as well as in 25(OH)D3 and 24,25(OH)₂D3 were observed.We conclude that (1) 1,25(OH)₂D3 may be reduced early in thecourse of chronic renal failure and that (2) because of abnormaldependence of 1 ,25(OH)₂D3 on 25(OH)D3, low 25(OH)D3 may resultin reduced 1,25(OH)₂D3 values post transplant. Increased PTHin such cases suggests the functional significance of theseobservations.