Kidneys, electrolytes and minerals
Potassium blood test: what a high or low result means
What a potassium blood test measures, what high or low potassium can mean, and what to ask your doctor.
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Explain my results → Available on web, iOS & Android.What is potassium?
Potassium is a mineral, also called an electrolyte, that helps your nerves and muscles work, including your heart muscle. Your kidneys keep the level in your blood within a narrow range. Potassium is measured in the U&E (urea and electrolytes) blood test, or a metabolic panel in the US, and appears on reports as K or K+.
Why is this test done?
- As part of a routine kidney blood test
- To monitor medicines that affect potassium, such as some blood pressure tablets and water tablets
- When someone has vomiting, diarrhoea or is unwell
- To monitor kidney disease
What does a high potassium mean?
A high potassium is called hyperkalaemia (hyperkalemia in the US). A very high level can affect the heart rhythm, so doctors take it seriously and often repeat the test quickly.
Possible reasons include:
- A sample that was difficult to take or delayed getting to the lab, which can falsely raise potassium
- Kidney disease
- Some medicines, such as ACE inhibitors, angiotensin receptor blockers and some water tablets
- Potassium supplements or salt substitutes
- Severe dehydration causing reduced kidney function (acute kidney injury)
What does a low potassium mean?
A low potassium is called hypokalaemia (hypokalemia in the US). It can cause weakness, cramps and, if very low, heart rhythm problems.
Possible reasons include:
- Water tablets (diuretics)
- Vomiting or diarrhoea
- Some hormone conditions
- Laxative overuse
- Not eating enough
Why we don't list a "normal range". Reference ranges differ between laboratories and can depend on your age, sex and whether you are pregnant. The range printed next to your result on your own report is the one that applies to you, so use that, and talk to your doctor about what your result means for you.
What can affect your potassium result?
- How the blood sample was taken and how quickly it reached the lab, which can make potassium look falsely high
- Clenching your fist repeatedly during the blood test
- Medicines that raise or lower potassium
- Kidney function
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Try it with your own results → Paste, upload or photograph your results.Questions to ask your doctor
- Could my result be due to the way the sample was taken, and should it be repeated?
- Do any of my medicines need to be changed?
- Should I change my diet?
- How soon should it be rechecked?
Frequently asked questions
Why might my doctor ask me to repeat a potassium test urgently?
A very high or low potassium can affect your heart rhythm. Also, potassium can look falsely high if blood cells in the sample burst, which can happen when a sample is difficult to take or delayed. A quick repeat confirms the true level.
What foods are high in potassium?
Bananas, potatoes, tomatoes, dried fruit, beans and many fruit juices are high in potassium. Do not change your diet based on a single result without advice from your doctor or dietitian.
What does haemolysed mean on my potassium result?
It means some red blood cells in the sample burst, releasing potassium and making the result unreliable. The test usually needs to be repeated.
Can Patiently AI explain my potassium result?
Yes. Paste your results, or upload a photo, PDF or Word file, and Patiently AI explains them in plain English, sticking to the numbers and ranges on your own report rather than adding its own, and suggests questions to ask your doctor. It is free, needs no account, and removes identifying details on your device first.