proximal renal tubular acidosis (RTA), an abnormal condition characterized by excessive acid accumulation and bicarbonate excretion. It is caused by the defective reabsorption of bicarbonate in the proximal tubules of the kidney and the resulting flow of excessive bicarbonate into the distal tubules, which normally secrete hydrogen ions. This disruption impedes the formation of titratable acids and ammonium for excretion and ultimately leads to metabolic acidosis. Treatment is the same as for renal tubular acidosis. In primary proximal RTA the defective reabsorption of bicarbonate is the sole causative factor. In secondary proximal RTA the resorptive defect is one of several causative factors and may result from tubular cell damage produced by various disorders, such as Fanconi’s syndrome. Compare distal renal tubular acidosis.
