Abnormalities of Calcium Metabolism in Patients on Hemodialysis: Changes of Ionized-calcium, Calcium-regulating hormones and Acid-base Balance During Hemodialysis

Abstract

To clarify the abnormalities of calcium metabolism in chronic renal failure patients maintained on hemodialysis, the calcium-related hormones and acid-base balance were measured in 46 patients before and during hemodialysis with a dialysate containing 7mg/dl of calcium. Before dialysis, the mean percentage of plasma ionized-calcium to plasma total calcium was high from acidosis, though both were within normal limits. The plasma inorganic phosphate level which was mostly high, correlated with the plasma parathyroid hormone (PTH) level. The plasma PTH and plasma human calcitonin levels were mostly high, but they did not correlate with the ionized-calcium level. A positive correlation was noted between plasma 25-hydroxycholecalciferol and plasma totalcalcium levels. Metabolic acidosis was observed in 24 patients, metabolic acidosis with respiratory compensation in 21, and respiratory acidosis in one. During hemodialysis, plasma PTH level decreased in 21 patients, but the overall mean did not. The mean levels of plasma albumin and arterial pH were elevated, At the completion of hemodialysis, 9 patients had respiratory alkalosis due to hyperventilation ; the plasma ionized-calcium level did not increase as a whole, but was markedly high in 3 patients. On the other hand, the mean plasma total calcium level, which increased significantly during hemodialysis, was remarkably high at the completion in 13 patients. The changes during hemodialysis in the plasma total calcium and plasma albumin levels correlated. These findings suggest that 7 mg/dl of calcium is not enough to prevent PTH hypersecretion in chronic renal failure. However, a dialysate containing more calcium may cause dangerous hypercalcemia. Therefore to prevent hypocalcemia and secondary hyperparathyroidism, adequate hemodialysis, and oral intake of aluminium hydroxide to correct hyper-phosphatemia and of activated vitamin D3 to increase intestinal calcium absorption are necessary.