Renal hypercalciuria and acidification defect in kidney stone patients

Calcium metabolism and renal acidification ability were examined in renal stone patients. On a random diet 33 of 52 patients excreted more than 4 mg. per kg. body weight per day of urinary calcium and were entered into a second study on a 300 mg. calcium diet. Absorptive and renal hypercalciuria was differentiated by fasting urinary calcium (mg. per 100 ml. glomerular filtration). Every absorptive hypercalciuria patient tested and 5 renal hypercalciuria patients had a normal renal acidification ability, and the serum parathyroid hormone and urinary cyclic adenosine monophosphate levels were normal. By calcium restriction urinary calcium decreased more in absorptive hypercalciuria than in renal hypercalciuria (2.48 +/- 0.14 versus 3.34 +/- 0.27 mg. per kg. body weight per day, p less than 0.05). However, urinary calcium remained high in 76 per cent of the patients with absorptive hypercalciuria. Nine patients had a defect in renal tubular acidification and the calcium metabolism was similar to those with renal hypercalciuria. Present studies show that renal hypercalciuria and renal tubular acidification defect cannot be differentiated without an ammonium chloride test.