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

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Abstract
Distal renal tubular acidosis was reported as an uncommon cause of urinary Ca stone disease. This defect appears to be more frequent when appropriate tests are performed systematically. Twenty-nine patients with recurrent Ca stones were separated into 3 groups: normocalciuric (group A), renal hypercalciuric (group B) and absorptive hypercalciuric (group C). Distal tubular functions were investigated by the (urine-blood) pCO2 [CO2 partial pressure] gradient and by an ammonium chloride test. (Urine-blood) pCO2 gradient was (mean .+-. SEM [standard error of the mean]), 3.33 .+-. 0.59 in group A, 2.95 .+-. 0.34 in group B and 3.31 .+-. 0.58 kPa [paschal] in group C. All these values differ significantly from those observed in controls (4.11 .+-. 0.28 kPa; P < 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 .mu.mol min-1 in group C. Values obtained in the first 2 groups were significantly lower than that achieved by control subjects (76.4 .+-. 14.9 .mu.mol min-1). Tubular dysfunctions defined as impairments in hydrogen ion secretion and ammonium excretion after an acid challenge are a common feature of the urinary Ca stone disease and play a contributory role in its pathogenesis.