Potassium
Potassium is a mineral that helps keep your heart beating steadily and your muscles working smoothly. Your kidneys hold it within a tight range, because both too much and too little can upset your heart rhythm. A result inside the range is reassuring; a result outside is worth a chat with your GP to find out why.
Standard CareWhat is potassium?
Potassium is an electrolyte — a charged mineral that your cells use to transmit electrical signals. It works in close partnership with sodium: while sodium is the main electrolyte outside cells, potassium is the main one inside. Together they drive the tiny electrical pulses that let your nerves fire and your muscles act. The RCPA describes potassium's dual role neatly: "potassium and sodium are needed to make nerve signals such as those telling your muscles to contract and relax," and "potassium is important in keeping your heart rhythm steady." Because the heart is a muscle that never stops, the level of potassium in the blood is watched carefully — both a high level (hyperkalaemia) and a low level (hypokalaemia) can disturb the heart's electrical rhythm.
Why is it tested?
Potassium is checked as part of routine electrolyte testing alongside sodium, chloride, and bicarbonate, and often alongside kidney markers such as creatinine and eGFR (estimated glomerular filtration rate — how well your kidneys are filtering). Your GP may order it as part of a standard health check, when investigating symptoms such as muscle weakness or palpitations (a noticeable or irregular heartbeat), or to monitor the effect of medicines that are known to shift potassium levels. Kidney disease, heart disease, and certain medicines are the most common reasons for repeated monitoring.
Reference range (Australia)
The AHRIA harmonised reference interval (AACB/RCPA-endorsed) applies to adults of all sexes. The range printed on your report is the figure your GP uses for your result — use that range when reading it.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A potassium below the reference range is called hypokalaemia. Common causes include fluid losses (vomiting, diarrhoea, or heavy sweating), diuretics (fluid tablets that cause the kidneys to pass more potassium in the urine), and some other medicines. Mild hypokalaemia may not cause any symptoms; a more significant drop can cause muscle cramps, weakness, or a sense that your heart is fluttering. Your GP will look at the likely cause and decide whether any change is needed.
A potassium within the reference range suggests your kidneys are keeping this electrolyte well balanced. Staying well hydrated and letting your GP know about any new medicines — particularly blood-pressure or diuretic medicines — is the best way to keep an eye on it over time.
A potassium above the reference range is called hyperkalaemia. On a routine test a mildly raised potassium often has a straightforward explanation, such as the blood draw itself or a medicine. A genuinely high level matters because it can affect the heart's rhythm, so your GP will check your kidney results and medicine list and may arrange a prompt repeat test. Kidney function plays a big role, since the kidneys are responsible for clearing excess potassium, so any reduction in kidney filtering can push the level up, and some medicines also raise it. A tricky blood draw is worth noting too, because a damaged or haemolysed (that is, broken-down) sample can give a falsely elevated reading.
What can affect your result
The kidneys are the main regulator of blood potassium, so anything that reduces kidney function can cause it to rise. On the medicine side, ACE inhibitors and ARBs (common blood-pressure medicines) tend to raise potassium; diuretics (fluid tablets) tend to lower it. Dietary potassium (from foods like bananas, potatoes, leafy greens, and legumes) usually has a modest effect on blood potassium in people with normal kidney function, because healthy kidneys adjust. In people with reduced kidney function, however, dietary potassium matters more and your GP may have specific advice. Significant fluid losses — from vomiting, diarrhoea, or heavy sweating — can lower potassium. The acid-base balance of your blood also influences potassium: as the RCPA notes, "changes in acid and alkaline levels in your blood, known as the acid-base balance, can affect electrolyte levels particularly those of potassium and bicarbonate."
When to act
If your potassium sits outside the reference range, that is worth mentioning to your GP rather than acting on yourself. A mildly raised or low result on a routine check is common and often has a simple explanation. If a result is markedly outside the range, or you have symptoms alongside it such as palpitations, significant muscle weakness or cramping, it is worth being seen sooner rather than waiting for a routine appointment. Your GP will decide whether to repeat the test or investigate further. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
Test your potassium
NATA-accredited testing. Results in 2–5 days. No GP referral required.
View UEC