The urine pH: a potentially misleading diagnostic test in patients with hyperchloremic metabolic acidosis

The purpose of this case report is to illustrate that the urine pH may be a misleading index in the assessment of the normal renal response to metabolic acidosis. On presentation, the patient had a normal anion-gap type of metabolic acidosis; the cause of the acidosis was gastrointestinal bicarbonate loss. Since the urine pH was 6.0 when the patient was acidemic, distal renal tubular acidosis was also suspected. However, since the kidneys generated more than 190 mmol of bicarbonate per day (urine ammonium was 190 mmol/d), reduced renal acid excretion was not the cause of the acidosis. Therefore, the urine pH of 6.0 provided a false clue with respect to a renal cause for the acidosis in this setting; in contrast, the urine anion gap provides more reliable information concerning bicarbonate generation by the kidney.