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Study of renal function on regulation of acid-base state
Last reviewed: 07.07.2025
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Maintenance of the acid-base balance with the preservation of a stable pH of arterial blood is carried out by homeostatic mechanisms, which are based on the physicochemical properties of blood and tissues, as well as physiological processes occurring in the lungs, kidneys, liver and gastrointestinal tract (GIT).
In clinical practice, to assess the ability of the kidneys to maintain acid-base balance, urine pH, ammonia secretion, titratable acid secretion, and bicarbonate excretion are studied.
In a healthy person, the pH of urine under normal conditions fluctuates between 4.5-7.5, often shifting to lower values (to the acidic side). Overloading with meat food promotes the release of more acidic urine, while a vegetable diet and abundant alkaline drinks significantly increase the pH of urine.
Excretion of titratable acids characterizes the amount of secreted hydrogen ions associated with phosphate anions and weak organic acids. It is determined by titrating urine with an alkali solution to the pH level of the blood.
Normally, the excretion of titratable acids is 10-30 mmol/day, or 7-21 μmol/min; the excretion of bicarbonates is 1-2 mmol/day; the secretion of ammonia is 30-60 mmol/day (21-35 μmol/min).
Ammonia, by binding with hydrogen, promotes the excretion of anions of strong acids (in the form of ammonium salts). Anions of weak acids are excreted in the form of titratable acids. The total excretion of acids by the kidney - the total excretion of H + - is 40-90 mmol/day.
The limit of acid excretion is the level of titration acidity and ammonia excretion at which urine pH reaches 4.5. At urine pH below 6.0, i.e. under conditions of complete reabsorption of bicarbonates, the total excretion of hydrogen ions is the sum of the daily excretion of ammonium and titratable acids.