Chemistry / Electrolytes
PotassiumK⁺
Principal intracellular cation; small shifts have large electrophysiologic effects.
Sample
Serum or plasma (lithium-heparin slightly lower than serum)
Clinical reference range
3.5 to 5 mmol/L
Adult
Conv: 3.5–5 mmol/LFunc: 4–4.7 mmol/L
Biology
What it measures
98% intracellular; regulated by aldosterone, insulin, β-adrenergic tone, and acid-base status. Renal excretion is the principal long-term mechanism.
Clinical use
Why we order it
Detect arrhythmia risk, monitor RAAS blockers and diuretics, evaluate adrenal disease.
Lens · Clinical
Interpretation by lens
Clinical interpretation
ECG changes (peaked T, widened QRS, sine wave) drive urgency more than the absolute number.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Renal failure
- ↑RAAS blockade (ACEi, ARB, MRA)
- ↑Trimethoprim, NSAIDs, heparin
- ↑Acidosis (intracellular shift out)
- ↑Tumor lysis, rhabdomyolysis, hemolysis
- ↑Pseudohyperkalemia (clenched fist, hemolysis, severe leukocytosis/thrombocytosis)
Causes of LOW
- ↓Diuretics (loop, thiazide)
- ↓GI loss (vomiting, diarrhea, laxatives)
- ↓Hyperaldosteronism (with HTN and metabolic alkalosis)
- ↓Insulin overdose, β-agonists
- ↓Magnesium depletion (will not correct K without correcting Mg)
Pitfalls
Pre-analytic & interpretation traps
- !Pseudohyperkalemia is extremely common — always re-draw with a free-flowing venipuncture before treating.
- !Hypomagnesemia must be corrected first or hypokalemia is refractory.
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