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Potassium
The potassium concentration in blood. Only a small fraction of the body's potassium is in the bloodstream, but that fraction is tightly controlled because heart and nerve cells depend on it. Small deviations matter more here than for almost any other routine test.
General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.
Usual adult reference range
The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.
| Group | SI units (mmol/L) | Conventional (mEq/L) |
|---|---|---|
| Typical adult reference interval | 3.5-5.1 | 3.5-5.1 |
Source: Typical adult reference interval published by clinical laboratories; serum and plasma intervals differ slightly. · checked 2026-09-02
What a high result generally indicates
The first thing a laboratory considers with a high potassium is whether the sample was haemolysed — red cells damaged during collection release potassium and produce a falsely high result. Genuine elevation is important: it is seen in kidney disease and with several common medicines, and at high levels it affects heart rhythm.
What a low result generally indicates
A low potassium is commonly caused by diuretics, by vomiting or diarrhoea, and by some hormonal conditions. It can cause muscle weakness, cramps and heart rhythm disturbance, and it often travels with a low magnesium that has to be corrected too.
These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.
What affects this result
- Sample handling — haemolysis is the single commonest cause of a spuriously high result.
- ACE inhibitors, ARBs, spironolactone and some others raise it.
- Loop and thiazide diuretics lower it.
- Kidney function: reduced filtration raises it.
- Potassium-based salt substitutes raise it.
- A clenched fist during the blood draw raises it locally.
Before the test
No fasting needed. Sample handling matters more than preparation.
Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.
The one thing to take from this page
The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.
Frequently asked questions
What is the normal range for potassium?
A typical adult reference interval is 3.5–5.1 mmol/L, but laboratories differ — the range printed on your own report is the one to use. And a result inside or outside a range is only meaningful in context, which is your doctor's reading, not a web page's.
What does a high potassium mean?
The first thing a laboratory considers with a high potassium is whether the sample was haemolysed — red cells damaged during collection release potassium and produce a falsely high result. Genuine elevation is important: it is seen in kidney disease and with several common medicines, and at high levels it affects heart rhythm.
What does a low potassium mean?
A low potassium is commonly caused by diuretics, by vomiting or diarrhoea, and by some hormonal conditions. It can cause muscle weakness, cramps and heart rhythm disturbance, and it often travels with a low magnesium that has to be corrected too.
Other markers
Haemoglobin
Hb, HGB
Ferritin
Serum ferritin
Vitamin D (25-OH)
25-hydroxyvitamin D, calcidiol
HbA1c
Glycated haemoglobin, A1c
Fasting glucose
Fasting plasma glucose, FPG
Total cholesterol
TC
All markers and the checker · Symptoms and nutrients · Medicine interactions
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