[Urinary acidification by furosemide test]

The aim of this study was to investigate the effect of furosemide on urinary acidification in 7 healthy children (aged 7 to 9 years) 5 patients with normokalemic distal renal tubular acidosis (RTA) (aged 4 to 13 years) and in 1 patient with proximal RTA (aged 20 months). Furosemide was given (2 mg/kg orally) as a tool to stimulate H+ and K+ secretion by enhancing Na delivery and transport in distal tubular segments. Patients with distal RTA were diagnosed by means of the ammonium chloride test and the alkaline overload and the one with proximal RTA by the ammonium chloride test only. Urinary acidification was evaluated 1 hour before and until 4 hours after furosemide administration. Healthy children (Fig. 1) showed a significant fall in urinary pH, 5.8 +/- 0.27 to 4.88 +/- 0.18 (p less than 0.02) and increase of NH3 excretion from 38.58 +/- 10.33 to 79.09 +/- 10.38 microEq/min/1.73 m2 (p less than 0.05). There was a direct correlation between urinary pH and urinary flow: r = 0.62 p less than 0.01 (Fig. 3). In patients with distal RTA (Fig. 5) furosemide failed to lower urine pH below 6 and net acid excretion persisted low: 47.9 +/- 6.1 microEq/min/1.73 m2. In the patient with proximal RTA (Fig. 4) furosemide produced the same effect as in healthy children with a fall in urine pH to 4.4 and an increase in net acid excretion to 118 microEq/min/1.73 m2. Furosemide proved to be effective to differentiate the type of RTA.(ABSTRACT TRUNCATED AT 250 WORDS)