Critical Potassium ValuesPotassium >6.5 mmol/L or <2.5 mmol/L is a cardiac emergency requiring urgent ECG and immediate treatment. Do not delay.
Causes of High Potassium (Hyperkalaemia)
| Cause | Mechanism |
|---|---|
| Renal failure | Kidneys cannot excrete potassium |
| ACE inhibitors / ARBs / spironolactone | Block aldosterone → potassium retention |
| Acidosis (DKA, metabolic) | H⁺ shifts K⁺ out of cells into blood |
| Haemolysis / haemolysed sample | Red cell contents released (check sample first) |
| Addison's disease | Lack of aldosterone → K⁺ retention |
| Rhabdomyolysis | Massive muscle breakdown releases K⁺ |
Causes of Low Potassium (Hypokalaemia)
| Cause | Mechanism |
|---|---|
| Loop / thiazide diuretics | Increased renal potassium excretion (most common) |
| Vomiting / diarrhoea | GI loss |
| Hypomagnesaemia | Required for potassium retention (fix Mg first) |
| Conn's syndrome (hyperaldosteronism) | Aldosterone drives K⁺ excretion |
| Insulin + glucose | Shifts K⁺ into cells (used to treat hyperkalaemia) |
Check the SampleHaemolysed blood samples falsely elevate potassium — always check if the sample was haemolysed before acting on a high result. Request a repeat if in doubt.
What ECG changes does high potassium cause?
Peaked T waves → widening QRS → sine wave pattern → ventricular fibrillation and cardiac arrest. ECG must be performed urgently in hyperkalaemia.
How is high potassium treated?
Calcium gluconate (cardiac membrane stabilisation — immediate), insulin + glucose (shifts K⁺ into cells — 30 min), calcium resonium or patiromer (gut binding — hours), dialysis for severe renal failure.
What are symptoms of low potassium?
Muscle weakness (may affect breathing at severe levels), cramps, fatigue, constipation, palpitations and arrhythmias, polyuria (blocks ADH action), and hypertension.
When does low potassium need IV treatment?
When K⁺ is <3.0 mmol/L, the patient is symptomatic (weakness, arrhythmia), or cannot take oral supplements. IV potassium must be given slowly (max 40 mmol/hr) on cardiac monitoring.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.