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Functional stress tests to assess renal acid excretion function
Last reviewed: 07.07.2025
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Of the acid loading tests, ammonium loading tests are most often used in the clinic. There are 2 versions of this test: with a single ammonium chloride load (0.1 g/kg body weight) - the Wrong and Davis test, a test with a long-term ammonium chloride load (0.1 g/kg body weight daily for 4-5 days) - the Elkinton test. The tests are assessed based on the degree of decrease in urine pH, excretion of titratable acids and ammonium.
The preservation of the acid-excreting function of the kidneys in the Wrong and Davis test is indicated by a decrease in urine pH below 5.3; the level of excretion of titratable acids above 25 μmol/min, excretion of ammonium more than 35 μmol/min and total excretion of hydrogen ions - more than 60 μmol/min.
In the Elkinton test, in healthy individuals, the urine pH is less than 5.0, the daily excretion of ammonium exceeds 60 mmol, hydrogen ions - 96 mmol, the total excretion of ammonium and titratable acids exceeds the initial level by more than 120 mmol/day.
Impaired renal acid excretion is characterized by high urine pH and decreased excretion of titratable acids and ammonium ions, which is inappropriate for the degree of systemic acidosis. Impaired ability to adequately reduce urine pH and decreased excretion of titratable acids are detected in renal tubular acidosis, hypokalemia, and hypercalciuria. In chronic renal failure and hypercalciuria, ammonium excretion is reduced.
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