Vitamin D metabolites in renal insufficiency and other vitamin D disorders of children.

Serum vitamin D metabolites were measured in relation to factors responsible for the synthesis of 1,25(OH)2D in children with renal disease and other disorders of vitamin D metabolism. Severe renal failure (CCr less than 15 ml/min/1.73 m2) was associated with a reduction in 1,25(OH)2D to 25% of mean normal levels, a very high PTH/1,25(OH)2D ratio of 75 (normal = 0.74), and a 60% reduction of serum 24,25(OH)2D. At CCr values between 15 and 50 ml/min 1.73 m2, 1,25(OH)2D was 50% of normal, despite a PTH/1,25(OH)2D ratio of 7 and a normal 24,25(OH)2D value. Above clearance values of 75 ml/min/1.73 m2, 1,25(OH)2D and the ratio were normal. Oral 1,25(OH)2D therapy in severe chronic renal insufficiency caused a fall in this ratio from 75 to 8. High PTH/1,25(OH)2D ratios were found in hypophosphatemic rickets and vitamin D-deficiency rickets, indicating reduced synthesis of 1,25(OH)2D relative to PTH. Low ratios were found in hypoparathyroidism and sarcoidosis, possibly indicating independence of PTH stimulation in 1,25(OH)2D production. The ratios of calcium/1,25(OH)2D and phosphate/1,25(OH)2D also provided useful information in each of these conditions, indicating that the use of such series of ratios in selected patients may promote a better understanding of pathogenic mechanisms and of the response to therapy.