Treatment of distal (type 1) and proximal (type 2) renal tubular acidosis
- Michael Emmett, MD
Michael Emmett, MD
- Editor-in-Chief — Nephrology
- Section Editor — Fluid and Electrolytes
- Chief of Internal Medicine
- Baylor University Medical Center
- Biff F Palmer, MD
Biff F Palmer, MD
- Professor of Internal Medicine
- University of Texas Southwestern Medical Center
The approach to therapy in distal (type 1) and proximal (type 2) renal tubular acidosis (RTA) is determined by the primary defect in each disorder: decreased distal acidification and impaired proximal bicarbonate reabsorption, respectively . Correction of the acidosis may have a variety of benefits, including restoration of normal growth in children , diminished renal potassium wasting and hypokalemia in distal RTA, stabilization or reversal of nephrocalcinosis, reduced frequency of calcium kidney stones, and possibly less osteoporosis in distal RTA and less rickets or osteomalacia in proximal RTA . Adequately treated patients are generally asymptomatic and able to lead a normal life, unless irreversible renal or bone disease has occurred prior to therapy.
The treatment of distal and proximal RTA will be reviewed here. The pathogenesis, etiology, and diagnosis of these disorders are discussed separately. (See "Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance" and "Etiology and diagnosis of distal (type 1) and proximal (type 2) renal tubular acidosis".)
DISTAL (TYPE 1) RENAL TUBULAR ACIDOSIS
Adults ingesting a typical American or Western European diet generate approximately 1 to 1.5 meq/kg of acid per day that is excreted by the kidneys in the form of titratable acids or ammonium. Patients with distal renal tubular acidosis (distal RTA) have a reduction in ammonium excretion and are unable to maximally lower the urine pH, resulting in the excretion of only part of the daily acid load. Thus, the daily alkali requirement is equal to the amount of hydrogen retained each day plus any urinary bicarbonate losses obligated by the high urine pH. The small amount of urine bicarbonate loss in patients with distal RTA is obligated by the relationship expressed by the Henderson-Hasselbalch equation. It does not represent a defect in bicarbonate reabsorption as in proximal RTA. If, for example, the urine pH is 6.4, the urine bicarbonate concentration will be approximately one-tenth (one log unit) that of the plasma or about 2 meq/L (assuming similar carbon dioxide tensions).
Correction of the metabolic acidosis has a number of beneficial effects. It restores normal growth rates in children, minimizes kidney stone formation and nephrocalcinosis, and diminishes calcium losses associated with bone buffering of some of the retained acid, thereby decreasing the risk of osteopenia. (See "Nephrolithiasis in renal tubular acidosis", section on 'Distal (type 1) RTA'.)
In addition, correction of the metabolic acidosis with alkali therapy (eg, sodium bicarbonate or sodium citrate) reduces inappropriate urinary potassium losses, which often corrects the associated hypokalemia [1,3-7]. Potassium depletion in these patients results from a reduction in proximal sodium reabsorption induced by metabolic acidosis [8,9]. The subsequent increase in sodium excretion leads to volume contraction and activation of the renin-angiotensin-aldosterone system. The combination of increased distal sodium delivery and aldosterone increases renal potassium excretion. (See "Overview and pathophysiology of renal tubular acidosis and the effect on potassium balance", section on 'Decreased net activity of the proton pump'.)
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