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Key Features

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  • Three subtypes of RTA are recognized

    • Type I or distal RTA: the classic form

    • Type II or proximal RTA: the bicarbonate-wasting form

    • Type III, or hyperkalemic RTA (rare in children): associated with hyporeninemic hypoaldosteronism or inherited in an autosomal manner

  • Types I and II and their variants are encountered most frequently in children

  • Type III is described historically as a combination of types I and II

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Clinical Findings

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  • Type 1 (distal RTA)

    • Failure to thrive, anorexia, vomiting, and dehydration

    • Hyperchloremic metabolic acidosis, hypokalemia, and a urinary pH exceeding 6.5 are found

    • Concomitant hypercalciuria may lead to nephrocalcinosis, nephrolithiasis, and renal failure

    • Some forms are associated with hearing loss

    • Distal RTA is often permanent

  • Type II (proximal RTA)

    • Characterized by failure to reabsorb bicarbonate appropriately in the proximal tubule with associated reduced serum bicarbonate concentration and normal anion gap hyperchloremic metabolic acidosis

    • Once a steady state is reached, the intact distal nephron appropriately excretes hydrogen ion, leading to a low urine pH

    • In the newborn can be considered an aspect of renal immaturity that improves with increasing gestational age

    • In infants is accompanied by failure to thrive and sometimes hypokalemia

    • Secondary forms result from reflux or obstructive uropathy or occur in association with other tubular disorders

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Diagnosis

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  • Diagnostic findings include

    • Normal anion gap

    • Hyperchloremic metabolic acidosis in the absence of diarrhea

    • Intravascular volume depletion

  • A concomitant urine pH is helpful in many cases; it is elevated in distal RTA despite the metabolic acidosis

  • The finding of hypophosphatemia or glycosuria should lead to further investigation of proximal tubular function (eg, Fanconi syndrome that is also associated with aminoaciduria)

  • A renal ultrasound should be obtained to exclude

    • Urinary tract obstruction (which can be seen with either proximal or distal RTA)

    • Nephrocalcinosis (seen in distal RTA)

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Treatment

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  • Citrate or bicarbonate supplementation is provided to target a serum bicarbonate level of 20–24 mEq/L, as an index of normal serum pH

  • Citrate solutions are more effective and often better tolerated than sodium bicarbonate

  • Due to bicarbonate wasting, children with proximal RTA typically require 5–20 mEq/kg/d citrate to achieve normal serum pH and bicarbonate concentration

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