Potassium (K) – Understanding Your Blood Test Result

Section Editors: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
September 15, 2026

Potassium is a mineral that carries a small electrical charge in your body. Minerals that behave this way are called electrolytes. Potassium stays mostly inside your cells, and the small amount in your blood stays within a narrow range because your heart and muscles depend on it to work properly. Your kidneys do most of the work of keeping it steady, removing any excess in your urine.

This article explains what the potassium test measures and what a high or low result can mean. It also explains why a difficult-to-collect sample can produce a falsely high reading.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What does the potassium test measure?

Potassium helps your cells send electrical signals. Nerves use those signals to communicate, muscles use them to contract, and the heart uses them to keep a steady rhythm. Because the heart is so sensitive to potassium, the body works hard to keep blood levels within a narrow band.

Only about two percent of your body’s potassium is in your blood. The rest is inside cells. So the blood result can change quickly when potassium shifts between the blood and the cells. The total amount in your body may not have changed at all.

Your report may show potassium in mmol/L or mEq/L, with a reference range printed next to it. These two units are equivalent for potassium. A typical adult level is about 3.5 to 5.0 mmol/L, and exact ranges vary by laboratory. Some reports show potassium simply as K, its chemical symbol.

Why can a potassium result be falsely high?

This is worth knowing before you read your own result, because it is common and can cause unnecessary worry.

Potassium leaks out of blood cells if they are damaged after the sample is taken. Several things can do this. Examples include a difficult blood draw, a very thin needle, squeezing the arm too hard, leaving a tourniquet on too long, or a sample that gets cold. The laboratory measures what is in the tube, so the result comes back high even though your actual blood potassium was normal.

This is called a falsely raised, or spurious, result. Laboratories often spot it because the sample looks slightly pink, and many will add a comment to the report. When a high potassium result is unexpected, and you feel completely well, repeating the test is often the first step, and the second result is usually normal.

How is the potassium test performed?

Potassium is measured on a small sample of blood, usually taken from a vein in your arm. No fasting is needed. It is included in the basic metabolic panel, the comprehensive metabolic panel, and most kidney function testing, so it is one of the most frequently measured substances in medicine.

Because a poor collection can affect the result, the laboratory may ask for a repeat sample rather than report a value it does not trust.

What do potassium results mean?

Potassium is read alongside your other electrolytes, your kidney tests, and your medicines.

A normal potassium level — a result inside the reference range means your body is balancing potassium as expected.
A high potassium level — a result above the reference range is called hyperkalemia. Mild elevations are common and often caused by the sample itself or by a medicine. Higher levels matter because potassium affects the heart’s rhythm. A genuinely raised result is acted on quickly.
A low potassium level — a result below the reference range is called hypokalemia. It is most often caused by fluid loss from vomiting or diarrhea, or by diuretic medicines. It can cause muscle weakness and cramps, and like a high result,t it can affect heart rhythm if it is marked.

Because both directions can affect the heart, potassium is one of the results a laboratory will call a doctor about immediately if it is far outside the expected range. If your result was only slightly outside the range and nobody contacted you urgently, that itself is informative.

What conditions and factors can affect potassium?

Common reasons potassium can be high.

A difficult blood draw — as described above, the most common explanation for an unexpectedly high result.
Medicines — several common drug groups raise potassium, including some blood pressure medicines and potassium-sparing diuretics. Do not stop any medicine because of a blood test. Ask the doctor who prescribed it.
Reduced kidney function — the kidneys remove excess potassium, so when they filter less well, it accumulates.
Potassium supplements or salt substitutes — many salt substitutes are potassium chloride.
Tissue injury — a crush injury, severe burns, or significant muscle breakdown releases potassium from inside cells.
Poorly controlled diabetes — which can shift potassium out of cells and into the blood.

Common reasons potassium can be low

Vomiting or diarrhea — potassium is lost directly in the fluid.
Diuretic medicines — commonly called water pills, these increase potassium loss in the urine.
Not eating enough — prolonged poor intake, or feeding after a long period without food.
Low magnesium — potassium is hard to correct while magnesium is low, so the two are often checked together.
Some hormonal conditions — which cause the kidneys to lose more potassium than usual.

What other tests are ordered with potassium?

Sodium, chloride, and bicarbonate — the other electrolytes, read together as a pattern rather than individually.
Creatinine, urea, and eGFR — to see whether the kidneys explain the result.
Magnesium — particularly when potassium is low and difficult to correct.
An electrocardiogram (ECG) — not a blood test, but a tracing of the heart’s electrical activity, often done when potassium is markedly abnormal.

What happens after a potassium test?

A mildly abnormal potassium in someone who feels well is very often repeated, particularly when a difficult blood draw is suspected. Many repeat results are normal.

If the result is confirmed, your doctor looks for the cause. That usually means reviewing your medicines first, since medicines are one of the commonest explanations in both directions, and checking your kidney function. Treatment depends entirely on the cause and on how far outside the range the result is. Doctors treat markedly high or low potassium promptly because it can affect the heart, sometimes in hospital. A mild abnormality with a clear explanation is often managed by adjusting a medicine and repeating the test.

Questions to ask your doctor

What was my potassium level, and what is the reference range at this laboratory?
Could the way the sample was taken have affected this result?
Do you want to repeat the test, and if so, when?
Could any of my medicines be causing this?
Is my kidney function part of the explanation?
Should my magnesium be checked as well?
Are there foods or salt substitutes I should watch out for?
What symptoms should prompt me to contact you before my next test?