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Potassium
The electrolyte that keeps nerves, muscles, and the heart's rhythm working.
Other names: Serum potassium, KSection: Blood chemistry
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortThe normal range is 3.7–5.2 mEq/L (3.7–5.2 mmol/L). Both high and low potassium matter because the heart's rhythm depends on it.
Reference ranges
Group
Reference range
Adults
3.7–5.2 mEq/L (3.7–5.2 mmol/L)
Normal value ranges vary slightly among laboratories. High potassium is often the result of two or more causes acting together.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Potassium is an electrolyte — a mineral that carries an electric charge in body fluids. It is the most abundant electrolyte inside cells, and it keeps nerves firing, muscles contracting, and the heart beating in rhythm. The kidneys regulate it: excess potassium leaves the body in urine.
The blood test measures potassium in the fluid portion of the blood and is usually part of a basic or comprehensive metabolic panel. Providers also order it when they suspect metabolic acidosis (for example from uncontrolled diabetes) or alkalosis (for example from excess vomiting), and sometimes during attacks of paralysis.
One sampling detail matters more than any preparation: if it is hard to get the needle into the vein, the red blood cells can be injured during the draw and release their potassium into the sample, producing a falsely high result. An unexpected high value is therefore often confirmed with a second draw.
Results are reported in milliequivalents per liter (mEq/L); in millimoles per liter (mmol/L) in many countries — for potassium the two numbers are identical. Natural black licorice can lower potassium, so it should be avoided for at least two weeks before the test (most licorice products in the U.S. do not contain natural licorice — check the ingredients label).
When it is high
Kidney insufficiency or failureThe kidneys excrete potassium, so when they falter, potassium accumulates — the most important cause of hyperkalemia.
Certain medicinesACE inhibitors, ARBs, the potassium-sparing diuretics spironolactone, amiloride, and triamterene, and beta blockers can all raise potassium.
Cell injury and destructionCrushed tissue injuries, burns, surgery, blood transfusion, and red blood cell destruction release the potassium stored inside cells.
Acidosis and uncontrolled diabetesMetabolic or respiratory acidosis shifts potassium out of cells; poorly controlled type 1 diabetes is a related cause.
Adrenal disordersAddison disease and the very rare hypoaldosteronism reduce potassium excretion.
Dietary excessVery large amounts of potassium-rich foods or potassium supplements can raise the level, though this is not common. Hyperkalemic periodic paralysis is a rare inherited cause.
When it is low
Fluid lossAcute or chronic diarrhea, vomiting, and heavy sweating drain potassium from the body; excessive laxative use does the same.
DiureticsWater pills such as hydrochlorothiazide, furosemide, torsemide, and indapamide increase potassium loss in urine.
Adrenal disordersCushing syndrome and hyperaldosteronism drive potassium excretion up.
Kidney causesRenal artery stenosis and the rare renal tubular acidosis disturb potassium handling; kidney disease can lower as well as raise the level.
Low intake and other causesA diet too low in potassium (not common), alcohol use disorder, natural black licorice, and hypokalemic periodic paralysis also appear on the list.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Natural black licorice (avoid 2 weeks before the test)Diuretics, ACE inhibitors, ARBs, beta blockersDifficult blood draw (falsely high from red cell injury)Diarrhea, vomiting, sweating
How to prepare
Do not eat natural black licorice for at least two weeks before the test, because it may lower your level. Tell your provider about all medicines and supplements you take, including diuretics and blood pressure medicines.
When a retest makes sense
An unexpectedly high result is often repeated, because red blood cell injury during a difficult draw can fake hyperkalemia. Confirmed abnormal values lead to a search for the cause, and a urine potassium test may be added.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a nephrologist if a kidney cause is suspected. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: PotassiumKSerum potassiumPotassium serum
Units and conversion
Measured in: mEq/L
mEq/L=mmol/L
For potassium, 1 mEq/L = 1 mmol/L — the number stays the same, only the unit label changes. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Potassium lives mainly inside cells. If red blood cells are injured while the sample is taken — for example when the vein is hard to access — their potassium leaks into the sample and the result reads falsely high. A repeat draw settles it.
Is mEq/L different from mmol/L for potassium?
Only in name. For potassium, 1 mEq/L equals 1 mmol/L, so a result of 4.5 mEq/L is written 4.5 mmol/L on reports that use SI units.
Does licorice really affect potassium?
Natural black licorice can lower potassium levels, so it should be avoided for at least two weeks before the test. Most licorice products sold in the U.S. do not contain natural licorice — the ingredients label tells you.
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