Renal Tubular Acidosis

Renal Tubular Acidosis: Excerpt from The 5-Minute Pediatric Consult

Andres J. Greco, MD

Renal Tubular Acidosis - BASICS

Renal Tubular Acidosis - description

• Group of transport defects produced by a failure to reabsorb filtered bicarbonate (type II), or an inability to excrete the daily endogenous metabolic acid load (type I).
• Renal tubular acidosis (RTA) syndromes are characterized by a normal anion gap metabolic acidosis, hyperchloremia, and relatively normal renal function.
• Distal RTA (type I):
  • Produced by an impaired distal acidification and characterized by an inability to lower urinary pH maximally (<5.5) under systemic acidemia
  • The main defect is an inability to secrete hydrogen ions or a back-leak of secreted hydrogen ions in the collecting duct.
• Proximal RTA (type II):
  • May occur as a primary and isolated entity or be part of the Fanconi syndrome (glycosuria, phosphaturia, aminoaciduria)
  • Caused by an impairment of bicarbonate reabsorption in the proximal tubule due to a decreased renal threshold (normally 22 mmol/L in infants and 26 mmol/L in adults and children)
  • Distal acidification mechanisms are intact (these patients can decrease urine pH <5.5 and excrete adequate amounts of NH
• Distal hyperkalemic (type IV):
  • Most common type of RTA in adults and children
  • Most frequently observed in hyperkalemic states of aldosterone deficiency or resistance, either isolated or in the context of renal parenchymal damage

Renal Tubular Acidosis - epidemiology

Primary RTA are very rare conditions.

Renal Tubular Acidosis - risk factors

Renal Tubular Acidosis - genetics

• Type I RTA can be observed sporadically or as an autosomal dominant (chromosome 17q21–22) or recessive transmission with deafness (chromosome 2p13) or without deafness (chromosome 7q33–34)
• Type II RTA with Fanconi syndrome occurs with several autosomal recessive disorders: Cystinosis, Löwe syndrome, Wilson disease, tyrosinemia, hereditary fructose intolerance, and galactosemia.
• Hereditary type IV RTA (hyperkalemic ) is most frequently observed in children with pseudohypoaldosteronism type 1 or type 2 (Gordon syndrome).

Renal Tubular Acidosis - associated conditions

• Failure to thrive
• Rickets (when associated with hypophosphatemia)
• Nephrocalcinosis and renal failure
• Nephrolithiasis
• Hypokalemia or hyperkalemia (type IV)
• Mild episodes of intercurrent vomiting or diarrhea can produce severe metabolic acidosis with electrolytes imbalance.

Renal Tubular Acidosis - DIAGNOSIS

Renal Tubular Acidosis - signs & symptoms

• Failure to thrive
• Renal colic
• Bone pain or deformities
• Photophobia (cystinosis)
• Hypertension (RTA type IV secondary to renal parenchymal disease or Gordon syndrome)

Renal Tubular Acidosis - history

• Urine concentration deficit (polyuria/polydipsia, enuresis)
• Constipation
• History of severe dehydration or metabolic acidosis with mild gastroenteritis/vomiting
• Medications/Drugs (acetazolamide, amphotericin B, lithium)
• Family history

Renal Tubular Acidosis - physical exam

• General: Failure to thrive
• Head and neck: Bossing forehead, abnormal eye examination (cystine deposition, cataracts, Kaiser–Fleischer ring)
• Chest: Rachitic rosary (healed rickets)
• Abdomen: Hepatomegaly, enlarged kidneys
• Extremities: Bowing of legs, widening of epiphysis of wrists

Renal Tubular Acidosis - tests

The hallmark or RTA is a hyperchloremic metabolic acidosis with normal anion gap and a normal renal function.

Renal Tubular Acidosis - lab

• Serum electrolytes test:
  • Helps to identify the presence of normal anion gap (8–16 mEq/L), metabolic acidosis, hypokalemia, or hyperkalemia
  • When assessing for RTA, this test should be run STAT to decreased the chance of a false-positive result.
• Urinalysis: Evaluates for features of Fanconi syndrome (glycosuria) or renal disease (proteinuria)
• Serum creatinine: Helps to exclude renal failure
• Urine anion gap and urine pH:
  • If urine pH is <6.0, then type I RTA can be ruled out.
  • Negative urine anion gap (Cl > Na + K) is seen in GI losses and proximal RTA.
  • Positive urine anion gap is seen in distal RTA.
• Urine spot for calcium/creatinine ratio: Patients with RTA can have hypercalciuria.
• Tubular reabsorption of phosphate (TRP): TRP <60% can be seen in Fanconi syndrome and other causes of proximal RTA. Aminoaciduria can also be present.
• 24-hour urine for citrate, calcium, potassium, and oxalate: Hypercalciuria and hypocitraturia are risk factors for nephrocalcinosis and/or Nephrolithiasis.

Renal Tubular Acidosis - imaging

• Long bone films/rickets survey: Evidence for rachitic changes, bone age (when indicated)
• Renal ultrasound: Evaluates for renal dysplasia, nephrocalcinosis, Nephrolithiasis, or hydronephrosis

Renal Tubular Acidosis - differencial diagnosis

• Diarrhea
• Use of acetazolamide
• GI fluid losses: Ileal conduits, fistulas draining the small bowel, biliary tract, or pancreas

Renal Tubular Acidosis - TREATMENT

• Alkali administration is the primary therapy for children with RTA.
• Sodium/potassium citrate (Polycitra 2 mEq HCOSodium citrate (Bicitra 1 mEq HCOOlder children can take sodium bicarbonate tablets (7.7 mEq HCOPatients with type I RTA usually require 1–4 mEq/kg alkali therapy per day in 3–4 divided doses.
• Patients with type II RTA require considerably more alkali therapy (5–20 mEq/kg/d in 4–6 divided doses).
• The dosage of alkali in children with type IV RTA ranges from 1–5 mEq/kg/d, which is usually sufficient to correct the hyperkalemia.

Renal Tubular Acidosis - FOLLOW UP

• Patients with RTA should be closely monitored with frequent potassium and plasma bicarbonate levels until a steady state is reached.
• Normal growth may be attained after the metabolic acidosis is corrected.
• Untreated type I RTA can lead to renal failure by causing progressive nephrocalcinosis. Adequate alkali therapy is usually enough to avoid this complication.
• Patients with hypercalciuria should be monitored with spot urine calcium/creatinine ratio. Alkali therapy should be adjusted to maintain a ratio <0.2 mg/mg.
• Renal ultrasound follow-up is recommended in patients with nephrocalcinosis.

Renal Tubular Acidosis - patient monitoring

• Avoid hemolyzed specimens that may artificially increase the serum potassium and reduce the plasma bicarbonate levels.
• Administer alkali over several divided doses.
• Closely monitor patients during episodes of gastroenteritis to avoid dehydration and severe metabolic acidosis.

Renal Tubular Acidosis - bibliography

1. Chan J, Scheinman JI, Roth K. Consultation with the specialist: Renal tubular acidosis. Pediatr Rev. 2001;22:277–287.
2. Hanna J, Scheinman JI, Chan J. The kidney in acid-base balance. Pediatr Clin North Am. 1995;42:1365–1393.
3. Rodriguez-Soriano J. Renal tubular acidosis: The clinical entity. J Am Soc Nephrol. 2002;13:2160–2170.
Shapiro J, Kaehny W. Pathogenesis and management of metabolic acidosis and alkalosis. In: Schrier RW, ed. Renal and Electrolyte Disorders, 6th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2003:115–153.

Renal Tubular Acidosis - CODES

Renal Tubular Acidosis - icd9

588.8 Other specified disorders resulting from impaired renal function

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About Proximal Renal Tubular Acidosis

• Back to disease: Proximal Renal Tubular Acidosis: Introduction
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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