Distal renal tubular dysfunction: a common feature in calcium stone formers

Distal renal tubular acidosis has been reported as an uncommon cause of urinary calcium stone disease. However, this defect appears to be more frequent when appropriate tests are performed systematically. Twenty-nine patients with recurrent calcium stones have been separated into three groups: normocalciuric (group A), renal hypercalciuric (group B) and absorptive hypercalciuric (group C). Distal tubular functions were investigated by the (urine-blood) pCO2 gradient and by an ammonium chloride test. (Urine-blood) pCO2 gradient was (mean +/- SEM), 3.33 +/- 0.59 in group A, 2.95 +/- 0.34 in group B and 3.31 +/- 0.58 kPa in group C. All these values differ significantly from those observed in controls (4.11 +/- 0.28 kPa; P less than 0.05). After 3 days of ammonium chloride loading, ammonium excretion averaged 54.7 +/- 4.2 in group A, 54.4 +/- 4.3 in group B and 64.3 +/- 5.5 mumol min-1 in group C. Values obtained in the first two groups were significantly lower than that achieved by control subjects (76.4 +/- 14.9 mumol min-1). It is concluded that tubular dysfunctions defined as impairments in hydrogen ion secretion and ammonium excretion after an acid challenge are a common feature of the urinary calcium stone disease and play a contributory role in its pathogenesis.