The term renal tubular acidosis (RTA) is applied to a group of transport defects in the reabsorption of bicarbonate (HCO3_), the excretion of hydrogen ion (H_), or both. This condition was first described in 1935, confirmed as a renal tubular disorder in 1946, and designated "renal tubular acidosis" in 1951. The RTA syndromes are characterized by a relatively normal GFR and a metabolic acidosis accompanied by hyperchloremia and a normal plasma anion gap.