Kidney / U&E
Potassium blood test
A potassium blood test measures an electrolyte that keeps your nerves, muscles and heart working normally. It's part of the urea and electrolytes (U&E) panel, and because the body keeps potassium within a tight range, results outside it are taken seriously and interpreted alongside kidney function and your medicines.
- What it measures
- Potassium, an electrolyte for nerves, muscles and the heart
- Sample
- Venous blood sample
- Fasting
- Not required
- Also known as
- serum potassium, K+
- Included in 57 Health tests
- 8 panels, from £95
Potassium reference range
Guide only| Category | Guide range |
|---|---|
| Adults | 3.5–5.3 mmol/L |
Potassium is tightly regulated, mainly by the kidneys. A slightly high reading can sometimes be a sample artefact (from red cells breaking down in the tube), so a genuinely raised result is usually rechecked. It's interpreted with urea, creatinine and eGFR.
These are general UK adult guide ranges from public health sources, shown for orientation only. Reference ranges vary by laboratory, assay, age and sex, so your result is always interpreted against the range quoted by the analysing laboratory on your report.
What does a high potassium level mean?
A high potassium (hyperkalaemia) can affect the heart's rhythm, so it's taken seriously. Common causes include reduced kidney function and certain medicines (such as some blood-pressure drugs and diuretics).
A mildly high result can also be a sample artefact, so it's often rechecked before any conclusion, and interpreted alongside kidney markers.
What does a low potassium level mean?
A low potassium (hypokalaemia) can cause muscle weakness, cramps and, if marked, heart-rhythm changes.
Common causes include vomiting or diarrhoea, some diuretics, and other fluid and hormone imbalances.
When to consider a potassium test
- A general health or kidney (U&E) check
- Taking blood-pressure medicines or diuretics
- Known kidney disease, diabetes or heart conditions
- Muscle weakness, cramps or palpitations
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. A potassium test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.