Biomedical Sciencemiddle twist
A 29-year-old woman has a plasma bicarbonate concentration of 15 mmol/L (reference 22–29 mmol/L) and a normal anion gap. Her urine pH is 6.2 during bicarbonate depletion and falls to 5.2 after administration of ammonium chloride. Her urinary bicarbonate excretion is increased when plasma bicarbonate is restored. Which defect best explains this pattern?