Potassium
Primary intracellular mineral for heart rhythm, blood pressure, and muscle contraction
Also known as
Definition
Potassium is the most important intracellular cation and plays a central role in regulating the resting membrane potential, heart rhythm, muscle contraction, nerve impulse conduction, and blood pressure. The kidneys regulate potassium levels precisely. Hypokalemia and hyperkalemia can cause life-threatening cardiac arrhythmias and require rapid intervention.
| Parameter | Value |
|---|---|
| Unit | mmol/l (mEq/l) |
| Reference Range | 3.5–5.0 mmol/l |
Agree on your personal target range with your doctor.
↓ What a low value means
Hypokalemia (< 3.5 mmol/l) arises from diuretics, vomiting, diarrhea, laxative abuse, primary hyperaldosteronism, or inadequate intake. Symptoms: muscle weakness, cramps, cardiac arrhythmias (prolonged QT interval), constipation, fatigue. Life-threatening below 2.5 mmol/l.
↑ What a high value means
Hyperkalemia (> 5.0 mmol/l) occurs with kidney insufficiency, hypoaldosteronism, ACE inhibitors/ARBs, potassium-sparing diuretics, extensive hemolysis, or massive muscle breakdown (rhabdomyolysis). Cardiac risk: dangerous arrhythmias (ventricular fibrillation) at > 6.5 mmol/l.
✓ What can influence this value
The potassium value is influenced by kidney function, dietary potassium intake, and medications: diuretics can lower the value, while ACE inhibitors, ARBs, and potassium-sparing diuretics can raise it. Vomiting, diarrhea, and laxatives lead to potassium losses. Magnesium deficiency can sustain a potassium deficiency. Regarding measurement conditions, hemolysis of the blood sample can make the value appear elevated. The assessment is made by the treating doctor.
When to test
In every routine blood panel; mandatory with diuretic therapy, heart disease, kidney insufficiency, diabetes, ACE inhibitor/ARB use, vomiting/diarrhea, eating disorders, or peak athletic training. Exclude pseudohyperkalemia from hemolysis of the blood sample.
Frequently asked questions
Why is potassium so critical for the heart? +
Potassium determines the resting membrane potential of cardiac muscle cells. Too little potassium (< 3.5 mmol/l) lowers the resting potential and makes heart muscle cells hyperexcitable — the risk of ventricular arrhythmias rises. Too much potassium permanently depolarizes heart muscle cells and can cause cardiac arrest.
Does potassium really help with high blood pressure? +
Yes. Potassium increases sodium excretion by the kidneys and acts as a vasodilator. DASH diet studies show that increased potassium intake can lower systolic blood pressure by 3–6 mmHg. The WHO recommends > 3,500 mg potassium daily as a cardiovascular protective measure.
Can exercise lead to potassium deficiency? +
Intense exercise only minimally increases potassium loss through sweat, but can transiently alter levels through aldosterone activation and redistribution between intra- and extracellular compartments. Chronic potassium deficiency is rare in endurance athletes with a balanced diet. With cramps, also consider magnesium deficiency.
Potassium
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.