Updated: 12/15/2019

Renal Tubular Acidosis (RTA)

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Snapshot
  • A 7-year-old boy presents to his pediatrician for a wellness visit. The mother reports that the patient urinates frequently and does not appear to be as tall as his classmates. Upon further questioning, the patient's mother states he has episodes of constipation and muscle weakness. Physical examination is notable for growth failure. Laboratory testing is significant for hyperchloremic metabolic acidosis, hypophosphatemia, and hypokalemia. Urinalysis is notable for a urine pH < 5.5, aminoaciduria, and glucosuria. (Fanconi syndrome leading to a type II renal tubular acidosis.)
Introduction
  • Clinical definition
    • renal tubular dysfunction that results in a hyperchloremic and normal anion gap metabolic acidosis
      • there is a relatively normal glomerular filtration rate
 
Renal Tubular Acidosis
Type
Etiology
Pathogenesis Treatment Comments
Type II (proximal)
  • Fanconi syndrome
  • Carbonic anhydrase II deficiency
  • Medications
    • acetazolamide
    • ifosfamide
    • topiramate
  • Heavy metals
    • e.g., mercury, cadmium, copper, and lead
  • Multiple myeloma
  • Wilson disease
  • ↓ bicarbonate reabsorption in the proximal tubule
    • administer bicarbonate and urine remains basic 
  • Potassium citrate
  • Thiazide diuretics
  • Associated with hypokalemia
  • At risk of developing hypophosphatemic rickets
  • Urine pH is initially > 5.5 and then later becomes < 5.5
Type I (distal)
  • Sjogren syndrome
  • Rheumatoid arthritis
  • Anion exchanger gene mutations
  • Medications
    • lithium
    • ifosfamide
    • analgesics
    • amphotericin B
  • Defective hydrogen secretion
  • Sodium bicarbonate or sodium citrate    
  • Associated with hypokalemia
  • At risk of developing calcium phosphate stones
  • Urine pH > 5.5
Type IV (hyporeninemic hypoaldosteronism) 
  • Diabetic nephropathy
  • Mineralocorticoid deficiency
  • Sickle cell disease
  • Systemic lupus erythematosus
  • Medications
    • heparin
    • angiotensin converting enzyme (ACE) inhibitors
    • angiogensin receptor blockers (ARBs)
    • cyclosporine
    • TMP-SMX
    • potassium sparing diuretics
  • Hyperkalemia results in ↓ ammonia (NH3) synthesis
    • ↓ the capacity to carry acid
  • Treatment depends on the underlying cause
  • Associated with hyperkalemia
  • Urine pH < 5.5

 

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(M2.RL.15.20) A 64-year-old man presents to his primary care physician's office for a routine check-up. His past medical history is significant for type 2 diabetes mellitus, hypertension, chronic atrial fibrillation, and ischemic cardiomyopathy. On his last visit three months ago, he was found to have hyperkalemia, at which time lisinopril and spironolactone were removed from his medication regimen. Currently, his medications include coumadin, aspirin, metformin, glyburide, metoprolol, furosemide, and amlodipine. His T is 37 C (98.6 F), BP 154/92 mm Hg, HR 80/min, and RR 16/min. His physical exam is notable for elevated jugular venous pressure, an S3 heart sound, and 1+ pitting pedal edema. His repeat lab work at the current visit is as follows:

Sodium: 138 mEq/L, potassium: 5.7 mEq/L, chloride 112 mEq/L, bicarbonate 18 mEq/L, BUN 29 mg/dL, and creatinine 2.1 mg/dL.

Which of the following is the most likely cause of this patient's acid-base and electrolyte abnormalities?
Tested Concept

QID: 104294
1

Furosemide

9%

(4/43)

2

Chronic renal failure

35%

(15/43)

3

Glyburide

5%

(2/43)

4

Renal tubular acidosis

47%

(20/43)

5

Amlodipine

0%

(0/43)

M 6 E

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