Urine Acidification After Ammonium Chloride

Urine acidification is the net effect of HCO3– reabsorption, H+ secretion, and the presence of buffers. A defect in H+ secretion in the collecting duct causes distal renal tubular acidosis (dRTA). In patients with minimal reductions in HCO3–, urine acidification tests such as the NH4Cl test and the furosemide fludrocortisone (FF) test are used to reveal incomplete forms of dRTA.1-3 Patients with dRTA do not adequately lower their urine pH in response to these acidification tests. However, recent reports showed discrepant results between the NH4Cl and FF tests in a substantial number of patients with suspected dRTA.

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