What is type 4 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

This is the most common form of RTA in adults and results from aldosterone deficiency or resistance. The collecting duct is a major site of aldosterone action; there it stimulates Na+ reabsorption and K+ secretion in the principal cells and stimulates H+ secretion in the A-type intercalated cells. Hypoaldosteronism, therefore, is associated with decreased collecting duct Na+ reabsorption, hyperkalemia, and metabolic acidosis.

Hyperkalemia also reduces proximal tubular NH4+ production and decreases NH4+ absorption by the thick ascending limb, leading to a reduction in medullary interstitial NH3 concentration. This diminishes the ability of the kidneys to excrete an acid load and worsens the acidosis.

Because the function of H+ –ATPase is normal, the urine is appropriately acidic in this form of RTA. Correction of hyperkalemia leads to correction of metabolic acidosis in many patients, pointing to the central role of hyperkalemia in the pathogenesis of this acidosis.


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