renal tubular acidosis (RTA) type IV (distal RTA)

Etiology

• acquired condition generally caused by insufficient urinary buffers, generally NH3
• disorders of aldosterone metabolism (> 98% are associated with diabetes mellitus)
  • hyporeninemic hypoaldosteronism
  • resistance to aldosterone
  • isolated aldosterone deficiency
    • congenital enzyme deficiency
  • Addison's disease
  • pharmacologic agents
    • low renin, low aldosterone
      • NSAIDs
      • beta-blockers
      • cyclosporine A
      • tacrolimus
    • high renin, low aldosterone
      • heparin
      • ACE inhibitors
      • angiotensin II receptor antagonists
      • ketoconazole
    • aldosterone receptor antagonists
      • amiloride
      • spironolactone
      • triamterene
      • trimethoprim
      • pentamidine
      • eplerenone
    • lithium
• chronic tubulointerstitial nephritis
  • analgesic abuse
  • allergic interstitial nephritis
  • chronic pyelonephritis
  • sickle cell disease
  • medullary cystic disease
  • Sjogren's syndrome
  • lupus erythematosus
  • sarcoidosis
  • tuberculosis
  • leprosy
  • hypertensive nephrosclerosis
  • obstructive uropathy
  • renal transplant patients

Epidemiology

most common form of RTA

Pathology

• aldosterone deficiency or resistance
• insufficient urinary buffers, generally NH3
• reduced H+ & K+ secretion, metabolic acidosis, hyperkalemia
• azotemia

Clinical manifestations

• no osteomalacia
• no nephrolithiasis

Laboratory

• Urine pH: < 5.5 (usually)
• serum HCO3-: > 15 meq/L
• serum aldosterone normal, high or low
• serum potassium: hyperkalemia; serum sodium: hyponatremia
• normal 24 hour urine citrate
• generally decreased glomerular filtration rate
• azotemia (increased BUN & serum creatinine)
• normal anion gap
• positive urinary anion gap

Radiology

• abdominal ultrasound if obstructive uropathy is suspected

Management

• rule out obstructive uropathy - foley catheter
• correct hyperkalemia
  • K+ restriction to 40-60 meq/day & a loop diuretic or thiazide diuretic
  • kayexalate may be necessary (kayexalate has fallen out of favor)
    • patiromer or sodium zirconium cyclosilicate may be more appropriate
  • HCO3- 1.5-2.0 meq/kg/day may be required
  • Fludrocortisone (Florinef) 0.1-0.2 mg PO QD should be considered in patients with primary adrenal insufficiency
  • stop offending medications
    • ACE inhibitor
    • spironolactone

More general terms

• renal tubular acidosis (RTA)