Hyperparathyroidism associated with distal tubular dysfunction but intact reabsorption of protein in the proximal tubules.

The urinary output of beta 2-microglobulin was measured in ten hypercalcemic patients undergoing surgery because of hyperparathyroidism. In three subjects the beta 2-microglobulin excretion was abnormally increased and in seven patients it was normal before surgery. Three of these seven patients displayed markedly impaired distal tubular function with a reduced urinary concentration capacity. After surgery all patients became normocalcemic and the urinary concentrating capacities improved. The beta 2-microglobulin excretion, on the other hand, remained unchanged. Thus, hypercalcemia per se does not readily affect the proximal tubular function of reabsorbing low molecular weight proteins. "Tubular proteinuria", if found in patients with hypercalcemia, should be suspected to reflect damage to the kidney by additional mechanisms.