What is the pathogenesis of proximal (type 2) renal tubular acidosis (RTA)?

Updated: Oct 10, 2018
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

The hallmark of type 2 RTA is impairment in proximal tubular HCO3- reabsorption. In the euvolemic state and in the absence of elevated levels of serum HCO3-, all filtered HCO3- is reabsorbed, 90% of which is in the proximal tubule. Normally, HCO3- excretion occurs only when serum HCO3- exceeds 24-28 mEq/L. Patients with type 2 RTA, however, have a lower threshold for excretion of HCO3-, leading to a loss of filtered HCO3- until the serum HCO3- concentration reaches the lower threshold. At this point, bicarbonaturia ceases and the urine appears appropriately acidified. Serum HCO3- typically does not fall below 15 mEq/L because of the ability of the collecting duct to reabsorb some HCO3-.


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