Potassium
The main electrolyte inside cells, essential for heart rhythm and muscle function.
| Typical reference range | 3.5–5.3 mmol/L |
| Commonly cited optimal range | 4–5 mmol/L |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
About 98% of the body's potassium is inside cells. The small amount in blood is tightly regulated by the kidneys under the influence of aldosterone and insulin.
Why it matters
Both high and low potassium can disturb heart rhythm, cause weakness and, at extremes, become dangerous. It is monitored closely in people taking diuretics, blood pressure medicines or with kidney disease.
What a high result can mean
High potassium can come from kidney disease, ACE inhibitors, ARBs, spironolactone, NSAIDs, potassium supplements, adrenal insufficiency or tissue breakdown. Frequently it is falsely high from hemolysis during the draw, fist clenching, prolonged tourniquet use or delayed processing.
What a low result can mean
Low potassium commonly results from diuretics, vomiting, diarrhea, laxative use, excess sweating, low magnesium, high aldosterone and insulin or beta-agonist use.
What affects the result
Sample handling is a major source of error; an unexpectedly high value is often repeated before acting on it. Diet (fruits, vegetables, legumes) and magnesium status influence levels. Interpret with magnesium, kidney function and medications.
Units and conversion
Usually reported in mmol/L.
- From mEq/L: multiply by 1 to get mmol/L
Also called on lab reports
K, Potassium, Serum, K+
Related tests: Electrolytes & Minerals
This page is educational and does not replace advice from a healthcare professional.