What it measures
Potassium is a salt in the blood that nerves and muscles, including the heart, need to work properly. Most of the body's potassium sits inside cells; the test reads the small amount in the serum around them.
Why people test it
- Part of a kidney or electrolyte panel, as the kidneys keep potassium in balance.
- Monitored on medicines that can raise or lower it, such as some blood pressure tablets and diuretics.
- Checked when there is muscle weakness, cramps or an irregular heartbeat.
Typical range
Ranges vary between labs, with the method used, age and sex, and your report shows the lab's own range. One NHS lab gives 3.5 to 5.3 mmol/L for serum. Source: North Bristol NHS Trust, Severn Pathology: potassium.
Finger-prick or vein?
A vein draw is usually advised. Finger-prick samples tend to read falsely high, because squeezing the finger damages red cells and releases their potassium, and delays in reaching the lab raise it too.
