Screening renal stone formers for distal renal tubular acidosis.

A group of 110 consecutive renal stone formers were screened for distal renal tubular acidosis (RTA) using morning fasting urinary pH (mfUpH) levels followed by a short ammonium chloride loading test in patients with levels above 6.0. In 14 patients (12.7%) a renal acidification defect was noted; 13 had incomplete and 1 had complete distal RTA. Distal RTA was found particularly in recurrent stone formers (17%), and especially in those with bilateral stone disease, where a distal renal tubular acidification defect was found in 50%. We have been unable to differentiate primary from secondary RTA in renal stone formers. Regardless of whether the acidification defect is primary or secondary to stone formation, however, all renal stone formers with distal RTA can expect to benefit from prophylactic alkaline therapy and it is recommended that the screening procedure, which is easy to use in daily clinical practice, is applied to all stone formers and not restricted to patients with recurrent stone disease.