Potassium

Also known as K, serum potassium

K⁺ inorganic ion

LOINC 2823-3 code verified serum mmol/L

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

A mineral that carries electrical charge inside your cells. Nerves and heart muscle depend on it being held in a narrow range.

No clinical version written yet.

if high unverified

Matters because it affects heart rhythm. Common causes are reduced kidney function and certain blood pressure medicines.

No clinical version written yet.

if low unverified

Often from fluid loss through vomiting or diarrhoea, or from water tablets. Causes cramps and weakness.

No clinical version written yet.

caveats unverified

If the blood sample is squeezed or shaken during the draw, potassium leaks out of the cells and the result reads falsely high. An unexpectedly high result with no symptoms is usually just repeated.

No clinical version written yet.

What this substance is

formula: K⁺
mass: 39.098 g/mol
monoisotopic: 38.96316
charge: 1
nucleus: 19 protons, 20 neutrons (39K)
electrons: 18: 1s² 2s² 2p⁶ 3s² 3p⁶
InChIKey: NPYPAHLBTDXSSS-UHFFFAOYSA-N
ChEBI: CHEBI:29103

Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.

3D model · Potassium

A schematic atom: a nucleus of 19 protons and 20 neutrons (the most common isotope, 39K), inside its electron shells, 1s² 2s² 2p⁶ 3s² 3p⁶. The configuration matches the NIST Atomic Spectra Database ground state of K II (1S0). The cloud is drawn as nested spheres because that term is an S state: the electron density really is spherical. Not to scale: shells are spaced on a square-root scale so the inner ones stay visible, and the nucleus is magnified about ten-thousand-fold.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm or the back of your hand. No special preparation is needed. Clenching and relaxing your fist over and over during the draw can raise the result for a short time. If the needle is hard to place, damaged red blood cells can release potassium and give a falsely high result.

Serum potassium is measured on a venous blood sample, usually as part of an electrolyte or metabolic panel, with no special preparation. Pseudo- hyperkalaemia can result from repeated fist clenching before or during venepuncture and from red cell injury (haemolysis) during a difficult draw. Many medicines interfere, and should not be stopped without the provider's advice.

Before the test

Avoid clenching and relaxing your fist repeatedly just before or during the blood draw.
Do not stop or change your medicines without talking to your provider first.

Where: laboratory

Sources: Potassium Blood Test -- MedlinePlus Medical Tests, U.S. National Library of Medicine; Potassium test -- MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

ion selective electrode

Direct ion-selective electrode

Much like the sodium measurement: a membrane that responds to potassium produces a small voltage which the machine reads.

A valinomycin-based membrane selective for K+.

What can throw it off

Haemolysis: red cells are rich in potassium, so any rupture in the tube raises the result. This is the single most common cause of an unexpectedly high potassium in someone who feels entirely well.

Avoid fist clenching during the draw and separate the sample promptly; both raise the result without anything being wrong.

Why labs disagree: Labs measure potassium with two kinds of electrode: most laboratory analysers use indirect ISEs, which dilute the sample first, while point-of-care devices use direct ISEs; this introduces a method-dependent difference in results. Handling also matters: because delayed sample transport affects potassium, some labs choose a higher upper reference limit (5.5 rather than 5.2 mmol/L) for practical reasons.

Sources: Discrepancies in Electrolyte Measurements by Direct and Indirect Ion Selective Electrodes due to Interferences by Proteins and Lipids. J Lab Physicians 2020 (PMC7467836); Tate JR et al. Opinion Paper: Deriving Harmonised Reference Intervals - Global Activities. EJIFCC 2016 (PMC4975217) cited · not yet checked by a person

What it reports on

nephron tubule regulated by
The kidney is mainly responsible for the body's potassium balance, and its tubules secrete potassium into urine.
adrenal gland regulated by
The adrenal glands make aldosterone, which tells the kidneys to get rid of potassium.

Associated symptoms

When low

low Muscle cramps or spasms · suggestive · common
low Muscles feeling weak · suggestive · common

Either direction

either Noticing your heartbeat · suggestive · occasional
Both ends of the range disturb cardiac conduction.
either Feeling tired all the time · non specific · occasional

Conditions this marker features in

When high

high High blood potassium · defining
Defined (European Resuscitation Council) as plasma potassium above 5.5 mmol/L; above 6.5 mmol/L is severe. There is no internationally agreed definition. A high result with normal kidney function should prompt a check for a false rise from cells breaking in the sample.
high Long-term reduced kidney function · monitoring
Checked regularly as kidney disease worsens; high potassium is a known complication.
high Sudden loss of kidney function · monitoring
High potassium is a dangerous complication of AKI and one of the usual reasons to start dialysis, so it is watched closely.

When low

low Low blood potassium · defining
Defined by a serum potassium below the normal range (below 3.5 mEq/L); below 2.5 mEq/L is severe.
low High blood sodium · supportive
Checked as part of the work-up. Low potassium (below 3.0 mmol/L) can stop the kidneys concentrating urine, leading to water loss.
low Low blood magnesium · supportive
Low potassium is common with low magnesium, and does not correct until magnesium is replaced.

Either direction

either Low blood sodium · supportive
Potassium helps find the cause: low potassium points to diuretics or vomiting, high potassium to adrenal insufficiency.

Ordered as part of

cmp · bmp · renal