Hyperkalemia: A Diagnostic Approach
Confirm before acting: potassium above the upper reference on one sample has important preanalytic causes.
Exclude pseudohyperkalemia
- Hemolysis in the sample falsely raises potassium.
- Delayed separation or prolonged tourniquet with fist clenching raises potassium.
- Thrombocytosis (platelet count above 500 x10^9/L) releases potassium during clotting.
- Leukocytosis with very high WBC releases potassium in vitro.
Mechanisms
- Redistribution: acidosis shifts potassium out of cells; beta-blockade, insulin deficiency, digoxin toxicity, and tissue breakdown (rhabdomyolysis, tumor lysis) also redistribute.
- Renal retention: acute or chronic kidney disease, type 4 RTA (hypoaldosteronism, ACE inhibitors/ARBs, potassium-sparing diuretics, NSAIDs, calcineurin inhibitors).
- Excess load: potassium supplements, salt substitutes, massive transfusion.
Decision points
Potassium above 5.5 mEq/L is hyperkalemia; above 6.0 mEq/L (or any level with ECG changes) is a medical emergency. Always correlate with ECG findings and chronical trends.