Hypokalemia (low potassium)
A lower-than-normal level of potassium in the blood. Because potassium keeps the heart and muscles working normally, a low level can cause muscle weakness, cramps and — when severe — dangerous heart-rhythm problems. It is often caused by fluid loss, diuretic medications or vomiting and diarrhoea.
What it is
Hypokalemia is a low level of potassium in the blood. Potassium is essential for the normal electrical activity of the heart and for muscle and nerve function, so keeping it in range matters. The commonest causes are losses from the body: through the gut (persistent vomiting or diarrhoea) or, very commonly, through the kidneys from diuretic (water) tablets, which are widely prescribed for blood pressure and heart failure. Other causes include a low magnesium (which makes potassium hard to correct until the magnesium is fixed too), certain hormonal conditions such as an excess of the hormone aldosterone (as in some causes of high blood pressure), some kidney tubular disorders, and potassium shifting into cells, for example during treatment of diabetic ketoacidosis or in a metabolic alkalosis. A mildly low level may cause no symptoms; a lower level causes muscle weakness, cramps, fatigue and constipation, and a significantly low potassium can disturb the heart's rhythm, which is especially concerning in people with heart disease or those on certain drugs. Because low potassium and low magnesium often go together and interact, both are usually checked and corrected together.
Key lab markers
- Potassium — the defining test.
- Magnesium — a low magnesium often accompanies it and must be corrected for potassium to normalise.
- Bicarbonate and chloride — help identify a metabolic alkalosis or the underlying pattern.
- Kidney function — context for cause and for safe correction.
- Sometimes aldosterone/renin — if a hormonal cause (as in resistant high blood pressure) is suspected.
Symptoms
- Often no symptoms if mild
- Muscle weakness, aches or cramps
- Fatigue
- Constipation
- Palpitations or an irregular heartbeat
- In severe cases, dangerous heart-rhythm disturbances
- Symptoms of the underlying cause (e.g. ongoing vomiting or diarrhoea)
Related symptoms
Related lab panels
When to discuss with a doctor
A mildly low potassium found on a routine test — often in someone taking a diuretic — is reviewed and usually corrected with dietary advice or supplements, and the medication is reconsidered, with the magnesium checked at the same time. A significantly low potassium, or a low level with muscle weakness, palpitations or an irregular heartbeat, needs prompt attention, especially in anyone with heart disease or on medications that affect the heart's rhythm, and severe hypokalemia is treated urgently. Persistent or unexplained low potassium is investigated for a cause, such as a hormonal condition or kidney problem. Mediora.AI can flag a low potassium and show it alongside magnesium and the acid-base markers so the pattern is visible, but the interpretation, and any correction, belong with your doctor.