Persistent and transient distal renal tubular acidosis with bicarbonate wasting

Bicarbonate titration studies were performed on two patients with bicarbonate wasting distal renal tubular acidosis (RTA; patients 1 and 2) and on three patients (3,4, and 5) with classic distal RTA. Daily requirements of alkali were 4.5 mEq/kg body wt in patient 1, a 3-year-old boy, and 16 mEq/kg in patient 2, a 5-month-old male infant. In contrast, only 1.5-2 mEq/kg/24 hr alkali were required in the three patients with classic distal RTA (age 8 1/2- 22 years). Patient 1 had glucose-6-phosphate dehydrogenase deficiency and patient 3 had inner ear deafness as an associated anomaly. In patient 2, the acidification defect was transient. Mean fractional excretion of bicarbonate (ChCO3-/Cin) times 100 at a plasma concentration of HCO3 below 20 mmol/liter was 5.1% in patient 1, 11.6% in patient 2, and 1.7% in patients 3-5. Minimal urine pH during the study was 7.38 in patient 1, 7.66 in patient 2, and 6.78-6.97 in the other patients. Values of net acid excretion at plasma HCO3 = 16 mmol/liter were strongly negative in patients 1 and 2 (-75 and -195 mumol/100 ml glomerular filtrate (GF), respectively) but slightly positive in the three patients with classic RTA (+3 to +20 mumol/100 ml GF). The two patients with bicarbonate wasting distal RTA were thus clearly separated from the group of patients with classic distal RTA.