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Why does potassium build up when kidneys fail?
Potassium is handled almost entirely by the kidneys — they excrete about 90% of your daily intake, and the gut handles the rest. As filtration falls, the kidneys compensate for a long time by dumping a larger share of what still reaches them.
That compensation runs out in later-stage CKD. Add a medication that blocks potassium excretion — an ACE inhibitor, ARB, or spironolactone — and blood levels can climb even on a modest diet.
Because high potassium affects heart rhythm before it causes any symptom you'd notice, this is one number you manage by lab result, not by feel.
About the author
Swetha Raju
Columbia M.S. Candidate in Clinical Human Nutrition · AKF Certified Kidney Health Coach · NKF Medical Advisory Committee (MAC) Member · NKF peer mentor · CKD patient advocate · Published chronic disease and nutrition researcher
Swetha Raju is the founder of NephroNourish. As a published researcher and lifelong chronic disease patient, she translates renal nutrition and metabolic science into practical guidance people can actually use.
A note on scope. This article is educational and not individual medical advice. Always discuss changes with your nephrologist, dietitian, or care team.