Also known as: blood potassium, kalaemia
Name: potassium, K
Related tests: Chloride, Electrolytes, Sodium
Why is the test done?
To detect and monitor acute or chronic hypokalaemia or hyperkalaemia.
When is the test done?
The test is performed routinely together with other electrolytes; it may be requested if symptoms such as weakness or cardiac arrhythmia are present, or when an acid–base or fluid and electrolyte imbalance is suspected. It is requested periodically if the patient takes medicines or has conditions (e.g. high blood pressure, kidney disease) that can alter blood potassium.
What samples are required?
A blood sample from a vein.
What is being analysed?
Potassium is a cation (a positively charged electrolyte) involved in generating the membrane potential and, together with other electrolytes such as sodium, chloride and bicarbonate, in maintaining the body’s fluid, electrolyte and acid–base balance. Potassium is the main intracellular cation: about 98% is inside the cells, while only about 2% is found in the interstitial fluids with which the plasma is in equilibrium. Changes in blood potassium concentration can have clinically important consequences, mainly for the heart muscle and skeletal muscles: how severe these are depends on the size of the change in concentration and on how quickly it develops.
How is the sample collected for testing?
The sample is taken from a vein in the arm.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Plasma potassium is often measured together with other electrolytes as part of a routine medical check-up. Hypokalaemia is rarely caused by insufficient dietary intake; the most frequent causes are kidney disease, certain medicines such as diuretics, diarrhoea, vomiting, heavy sweating,
and acid–base disorders; potassium measurement is used to monitor conditions associated with changes in blood potassium.
When is it requested?
As this electrolyte is important for heart and neuromuscular function in general, potassium is measured routinely during a medical check-up, especially if the patient is being treated with diuretics or heart medicines. The test is frequently requested in cases of high blood pressure or kidney disease, or when the patient is on dialysis.
What does the test result mean?
Hyperkalaemia, i.e. increased potassium in the blood, may be found in the following conditions:
- excessive intravenous or dietary intake (the latter is rare unless combined with conditions that impair the ability to eliminate potassium, such as kidney failure)
- acute or chronic kidney failure
- Addison’s disease or secondary hypoaldosteronism
- medicines such as ACE inhibitors, potassium-sparing diuretics, NSAIDs, beta blockers, digitalis
- extensive tissue damage, as in trauma or burns
- diabetes
Hypokalaemia, i.e. decreased potassium in the blood, may be found in the following conditions:
- vomiting
- diarrhoea
- use of diuretics
- diabetes, especially if poorly controlled
- hyperaldosteronism
- low dietary intake (rare)
Is there anything else I should know?
A high potassium value may depend on how the blood is drawn and how the sample is handled; bear in mind that potassium in the sample can increase when the patient clenches and unclenches their fist
vigorously during the blood draw, when the tourniquet is too tight, when the blood is drawn into the tube too quickly, or when the sample is not processed promptly. If the doctor has doubts about a high potassium result, they may ask for the test to be repeated.
1. What are the main dietary sources of potassium?
2. Are there kits on sale in pharmacies for measuring blood potassium?
1. What are the main dietary sources of potassium?
The main sources are fruit, vegetables and meat, especially when they have not been industrially processed for preservation.
2. Are there kits available in pharmacies for measuring blood potassium?
No. Electrolytes must be measured in a laboratory using high-sensitivity equipment.