## Pathophysiology of Hyperkalemia in CKD **Key Point:** The kidneys excrete 90% of dietary potassium; when GFR falls below 15 mL/min/1.73m², hyperkalemia becomes inevitable without dietary restriction or dialysis. ### Why Reduced Renal Excretion Is Most Common In chronic kidney disease, the primary mechanism of hyperkalemia is **impaired renal potassium excretion**. Even at GFR 20–30 mL/min/1.73m², the kidneys lose their ability to increase potassium secretion in response to a potassium load. - Aldosterone resistance develops in advanced CKD - Reduced distal tubular flow limits potassium secretion - Loss of functioning nephrons decreases total secretory capacity **High-Yield:** This is the dominant mechanism in ~90% of hyperkalemia cases in CKD stage 4–5, regardless of diet or acid–base status. ### Comparison of Other Mechanisms in CKD | Mechanism | Frequency in CKD | Comments | |-----------|------------------|----------| | Reduced renal excretion | ~90% | Primary, inevitable with low GFR | | Dietary excess | ~5–10% | Contributory, not primary cause | | Transcellular shift | <5% | Occurs with acidosis, but not the main driver | | Hemolysis/pseudohyperkalemia | <1% | Laboratory artifact, not true hyperkalemia | **Clinical Pearl:** A patient with CKD stage 4 will develop hyperkalemia even on a normal potassium diet if dialysis or medications (e.g., loop diuretics, fludrocortisone) are not used to augment excretion. ### Management Approach 1. **Confirm true hyperkalemia** — repeat sample, avoid hemolysis 2. **Assess renal function** — GFR is the strongest predictor 3. **Restrict dietary K⁺** — <2–3 g/day in advanced CKD 4. **Optimize medications** — avoid ACE-I, ARB, NSAIDs, K⁺-sparing diuretics 5. **Consider dialysis** — if GFR <15 mL/min/1.73m² and K⁺ persistently elevated **Mnemonic:** **REDUCED** — Renal excretion is the primary Etiology in CKD. (Dietary, Transcellular shift, Hemolysis are secondary.)
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.