Serum concentrations of metabolites of vitamin D in patients with chronic renal failure (CRF). Consequences for the treatment with 1-alpha-hydroxy-derivatives.

In forty-two patients with chronic renal failure (CRF), serum concentrations of 25-hydroxy-cholecalciferol (25-OHCC), 24,25-dihydroxy-cholecalciferol (24,25-OH2CC) and 1,25-dihydroxy-cholecalciferol (1,25-OH2CC) were measured before and during intermittent haemodialysis (IHD) and in a few cases also after renal transplantation. 25-OHCC and 24,25-OH2CC were measured by means of a competitive protein binding assay after Sephadex LH20 chromatography and 1,25-OH2CC by means of a radioimmunoassay after Sephadex LH20 and high pressure liquid chromatography (HPLC). In our patients serum values for 25-OHCC and 24,25-OH2CC showed a seasonal fluctuation as in normal individuals. The concentrations in the serum of 24,25-OH2CC and 1,25-OH2CC showed a positive correlation with renal function. With regard to 24,25-OH2CC this correlation was only found for the 24,25-OH2CC:25-OHCC ratio which was used to eliminate the seasonal fluctuation. For both dihydroxylated metabolites subnormal concentrations were found when the creatinine clearance was 40-50 ml/min and lower. It appears that the decrease of the plasma level of these metabolites of Vitamin D precedes (or is concomitant with) the changes in the serum values of calcium (Ca), phosphorus (P) and parathyroid hormone (PTH) and the diminution of the intestinal absorption of Ca. These findings indicate that patients with CRF should be treated at an early stage of the disease with 1 alpha-hydroxy-derivatives of Vitamin D in order to prevent the development of, or to induce the healing of, bone-lesions of renal osteodystrophy.