Potassium blood test
In short
A typical adult potassium result is 3.6 to 5.2 mmol/L. A slightly high potassium can come from how the blood was drawn, so doctors often repeat it. A true rise usually relates to the kidneys or medicines. Always read your result against the range printed on your own report.
A mineral salt (electrolyte) that keeps your heartbeat and muscles steady.
Potassium helps your heart keep a steady rhythm and your muscles and nerves work. The kidneys keep it in a narrow range. Levels too high or too low can affect the heartbeat, so doctors watch it closely.
Is my Potassium high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults | 3.6–5.2 | mmol/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your Potassium is high
A slightly high potassium can come from how the blood was drawn, so doctors often repeat it. A true rise usually relates to the kidneys or medicines.
Common reasons
- Blood cells breaking in the tube after a hard draw or a delay
- Some blood pressure medicines, some pain relievers or potassium-saving water pills
- Potassium supplements or salt substitutes
- Kidneys that filter less, as with long-term kidney disease
- Less often: very high blood sugar or acid buildup in the blood
- Less often: a problem with the adrenal glands, which sit above the kidneys
If your Potassium is low
A low potassium most often comes from water pills or from losing fluid through vomiting or diarrhea.
Common reasons
- Water pills (diuretics)
- Vomiting or diarrhea
- Heavy use of laxatives
- Eating very little, or few fruits and vegetables
- Low magnesium, which makes the body lose potassium
- Less often: adrenal glands making too much of a salt-balancing hormone
What can throw it off
A sample that was hard to draw or sat too long can read falsely high.
When it can’t wait
A Potassium of 6 mmol/L or more, or 2.5 mmol/L or less, usually needs a doctor's attention the same day. Call your doctor’s office, or their after-hours line. If you feel very unwell, call your local emergency number.
Questions to take to your appointment
- 1Could the way my blood was drawn explain this?
- 2Could my medicines, including any water pills, explain it?
- 3Should we repeat it soon, and check my magnesium too?
Read together with
Doctors rarely read Potassium alone. These usually sit next to it.
- SodiumA mineral salt (electrolyte) that keeps the body's water in balance.
- CreatinineA waste product from muscles that the kidneys clear.
- eGFRAn estimate of how much blood your kidneys filter each minute.
- CO2Mostly bicarbonate, which keeps your blood from becoming too acidic.
- MagnesiumA mineral that keeps muscles, nerves and the heartbeat steady.
Quick answers
What is the potassium blood test?
Potassium: A mineral salt (electrolyte) that keeps your heartbeat and muscles steady. Potassium helps your heart keep a steady rhythm and your muscles and nerves work. The kidneys keep it in a narrow range. Levels too high or too low can affect the heartbeat, so doctors watch it closely.
What is a normal potassium level?
For most adults, potassium is typically 3.6 to 5.2 mmol/L. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high potassium mean?
A slightly high potassium can come from how the blood was drawn, so doctors often repeat it. A true rise usually relates to the kidneys or medicines. Common reasons include blood cells breaking in the tube after a hard draw or a delay; some blood pressure medicines, some pain relievers or potassium-saving water pills; potassium supplements or salt substitutes; and kidneys that filter less, as with long-term kidney disease. A doctor reads it together with your other results and how you feel.
What does a low potassium mean?
A low potassium most often comes from water pills or from losing fluid through vomiting or diarrhea. Common reasons include water pills (diuretics); vomiting or diarrhea; heavy use of laxatives; and eating very little, or few fruits and vegetables.
What can affect my potassium result?
A sample that was hard to draw or sat too long can read falsely high.
When is my potassium result urgent?
A potassium result of 6 mmol/L or more, or 2.5 mmol/L or less usually needs a doctor's attention the same day. Call your doctor's office or their after-hours line. If you feel very unwell, call your local emergency number.
What should I ask my doctor about my potassium?
Questions worth taking to the appointment: Could the way my blood was drawn explain this? Could my medicines, including any water pills, explain it? Should we repeat it soon, and check my magnesium too?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- Mayo Clinic Laboratories — Potassium, serum
- MedlinePlus — Potassium blood test
- Mayo Clinic Laboratories — Critical values / critical results list
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.