THE FRUSEMIDE TEST - SIMPLE SCREENING-TEST FOR RENAL ACIDIFICATION DEFECT IN UROLITHIASIS

Urinary pH was first labelled as a risk factor for patients with recur rent calcium stone disease of the renal tract in 1978. The standard di agnostic test for patients with a history of stones, who appear to hav e urinary acidification defects is the ammonium chloride test. However , the performance of this test results in significant morbidity, parti cularly nausea and vomiting, and as a result there is little enthusias m for screening for such defects. We describe a screening test that ma y be used to determine which patients require more definitive testing. It involves an oral dose of frusemide (40 mg) followed by half -hourl y urine sampling for pH. For the detection of a renal tubular acidific ation defect, the frusemide test had sensitivity = 100%, specificity = 82%, predictive value of a positive result = 40%, predictive value of a negative result = 100%, screening efficiency = 84%, and there was n o morbidity. During the ammonium chloride test 80% of the patients vom ited or felt very nauseated.