Renal stone risk factors in patients with type IV renal tubular acidosis

Renal stone formation is uncommon in patients with type IV renal tubular acidosis (RTA). This study was undertaken to explore the urinary biochemical and physicochemical factors in patients with type IV RTA in order to elucidate the mechanisms that protect them from renal stone formation. Twelve subjects with type IV RTA and 12 matched subjects with a similar degree of kidney impairment but without RTA were studied. Both groups of patients had low urinary excretion of calcium, phosphorus, uric acid, and citrate, probably reflective of kidney impairment. Patients with type IV RTA had a significantly lower urinary pH and urinary excretion of calcium than their matched controls. Hypocitraturia was present in both groups without any significant difference between them. This study suggests that the major protection from renal stone formation in type IV RTA results from impaired renal function and ensuing reduction in renal excretion of stone-forming substances, such as calcium and uric acid.