Potassium blood test: normal range explained

Potassium is an electrolyte, a mineral that carries an electric charge in your blood. It helps control the balance of fluids and acids in the body, and it keeps nerves and muscles working. Almost all of your potassium sits inside cells, and the kidneys remove the extra in urine, so only a small amount is in the blood the test measures.

The test is usually part of an electrolyte panel, a kidney function test or a metabolic panel, where it is read beside sodium, chloride and creatinine.

Doctors order potassium at routine check-ups and to help diagnose or monitor kidney disease, high blood pressure and heart disease. It is also used to watch people who take medicines that affect potassium, such as diuretics (water pills), and people with diabetes or adrenal gland disorders.

Because a sample can be spoiled during collection, a doctor may repeat the test before acting on a surprising result.

A potassium result can move for reasons that have nothing to do with your kidneys or your diet, including how the blood was drawn.

• Clenching and releasing your fist repeatedly just before or during the blood draw can raise the result for a short time.
• Red blood cells that break during collection, a slow journey to the lab, or a tube with a potassium preservative can all falsely raise the result.
• Some medicines raise potassium, including ACE inhibitors, anti-inflammatory painkillers such as ibuprofen and potassium-sparing diuretics, while other diuretics lower it. Tell your doctor about every medicine you take.
• Fluid loss from diarrhoea, vomiting or heavy sweating can lower potassium, and kidney disease can push it either way.
• Natural black liquorice can lower potassium, so MedlinePlus advises avoiding it for at least two weeks before the test.
• In people with diabetes, potassium can fall after taking insulin, especially when blood sugar has been high for a while.
• Injuries, burns or surgery can release potassium from damaged cells and raise the level.