Calcium Metabolism in Renal Failure

Osteodystrophy is almost universally present in chronic renal failure. Mild, but detectable, abnormalities--especially in parathyroid hormone (PTH) secretion--occur even when the glomerular filtration rate is greater than 30 cc/min. Osteomalacia is common in areas in which vitamin D intake and exposure to sunlight are minimal; when these factors are plentiful, osteitis fibrosa predominates. Osteoporosis is seen with increasing frequency in hemodialyzed patients. Nonosseous complications of secondary hyper-parathyroidism include hypercalcemia, metastatic calcification and pruritus. The most important factor in the medical therapy of osteodystrophy is control of serum phosphate levels. Next, a positive calcium balance must be provided either by giving vitamin D as dihyrdotachysterol, raising dialysate calcium or administering calcium orally. Parathyroidectomy is sometimes indicated, especially when the patients are transplant candidates and manifest hypercalcemia. Whether or not transplant is contemplated, patients with persistently high calcium-phosphate products, severe metastatic calcification or rapidly progressive osteodystrophy should be considered for parathyroidectomy. Newer, experimental vitamin D preparations, such as 1,25-dihydroxycholecalciferol or 1-alpha-hydroxycholecalciferol, should improve the managemet of patients with renal osteodystrophy and decrease the need for parathyroidectomies.