Potassium
Potassium is the body's main intracellular electrolyte. Both high and low values are arrhythmia risks — every laboratory treats it as critical.
What it measures
Potassium is the dominant positively-charged ion inside your cells. The 30-fold gradient between inside and outside the cell is what makes nerve impulses and heart-muscle contraction work. Small changes in serum potassium cause large changes in cardiac excitability, which is why labs flag both ends of the range immediately. The kidneys do most of the regulation, helped by aldosterone; the gastrointestinal tract handles the rest.
What a high value can mean
- Kidney failure — the most common cause of significant hyperkalaemia.
- Medications — ACE inhibitors, ARBs, spironolactone, potassium-sparing diuretics, NSAIDs, trimethoprim.
- Cellular release — rhabdomyolysis, tumour lysis syndrome, severe burns, haemolysis.
- Adrenal insufficiency — low aldosterone.
- Spurious / pseudo-hyperkalaemia — sample haemolysis during draw is very common; repeat if isolated.
What a low value can mean
- Diuretics (thiazides, loop) — the most common cause.
- Gastrointestinal loss — vomiting, diarrhoea, laxative abuse.
- Renal loss — hyperaldosteronism, renal tubular acidosis.
- Magnesium deficiency — hypokalaemia is refractory to correction until magnesium is replaced.
- Insulin therapy, beta-agonists, alkalosis — shift potassium into cells.
When to discuss with a doctor
Potassium <3.0 or >6.0 mmol/L warrants urgent evaluation — these levels can trigger life-threatening arrhythmias. ECG is the next step. Mild abnormalities (3.0–3.4 or 5.1–5.9) warrant primary-care review and a repeat draw. Repeat values are essential because in-vitro haemolysis is a frequent false-positive.