type 4 renal tubular acidosis
Summary
Type 4 RTA is a hyperkalemic, normal anion gap metabolic acidosis caused by aldosterone deficiency or resistance, resulting in impaired distal nephron acid excretion. It's the most common form of RTA and often occurs in diabetic nephropathy or with ACE inhibitors.
Detail
Type 4 RTA results from aldosterone deficiency (hyporeninemic hypoaldosteronism) or aldosterone resistance at the collecting duct. Unlike other RTA types, it presents with hyperkalemia rather than hypokalemia. The pathophysiology involves impaired Na+ reabsorption and K+/H+ secretion in the collecting duct, leading to positive potassium balance and metabolic acidosis. Common causes include diabetic nephropathy (most common), chronic kidney disease, medications (ACE inhibitors, ARBs, heparin, NSAIDs), and primary adrenal insufficiency. Clinical features include mild metabolic acidosis (serum HCO3- typically 15-20 mEq/L), hyperkalemia, normal anion gap, and usually preserved GFR initially. Unlike types 1 and 2 RTA, nephrolithiasis and nephrocalcinosis are uncommon. Treatment focuses on addressing hyperkalemia with dietary potassium restriction, mineralocorticoid replacement (fludrocortisone), or potassium-wasting diuretics, while managing the underlying condition.
Sources
- First Aid for the USMLE Step 1 2024
- Harrison's Principles of Internal Medicine 21st Edition
- Brenner & Rector's The Kidney 11th Edition
- UpToDate: Renal tubular acidosis
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