What is a potassium test?
Serum potassium measures K+ in your blood. Potassium is mostly inside cells — only 2% is in blood, but this fraction is critical for heart rhythm, muscle contraction and nerve function. The kidneys regulate potassium by excreting excess in urine. It must be checked whenever you take diuretics, ACE inhibitors, ARBs, or digoxin.
Potassium normal range
| Level | Value (mEq/L) | Action |
|---|---|---|
| Critical low | < 2.5 | Emergency IV replacement |
| Low | 2.5 – 3.4 | Hypokalaemia — treat |
| Normal | 3.5 – 5.0 | Normal |
| High | 5.0 – 6.0 | Hyperkalaemia — monitor |
| Critical high | > 6.5 | Emergency — cardiac risk |
LOW Potassium — Hypokalaemia
Most commonly caused by: diuretics (furosemide, hydrochlorothiazide), vomiting or diarrhoea, poor dietary intake, excessive sweating, laxative abuse, corticosteroids, hyperaldosteronism. Symptoms: muscle weakness and cramps, fatigue, constipation, palpitations. ECG changes (U waves, flat T waves) and arrhythmias can occur especially with digoxin.
HIGH Potassium — Hyperkalaemia
Causes: kidney disease or failure (cannot excrete K+), ACE inhibitors, ARBs, potassium-sparing diuretics (spironolactone), NSAIDs, diabetic ketoacidosis, Addison disease, haemolysis or traumatic blood draw (pseudohyperkalaemia). ECG: peaked T waves, wide QRS, sine wave pattern, cardiac arrest. Above 6.5 mEq/L with ECG changes is a medical emergency.
Questions to ask your doctor
- Could this be a lab error from haemolysis?
- Is my diuretic or ACE inhibitor affecting my potassium?
- What foods should I eat or avoid?
- Do I need an ECG?
- How often should I recheck?