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Potassium Blood Test: What Your Results Mean

Potassium is the main electrolyte inside your cells (intracellular fluid) and plays a critical role in maintaining normal heart rhythm, muscle contraction, and nerve signalling. Even small deviations from the normal range can significantly affect the heart's electrical system, making potassium one of the most closely monitored electrolytes in clinical medicine.

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Normal Range

3.5 – 5.1 mmol/L

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Unit

mmol/L

What Your Results Mean

Normal

A normal potassium level indicates that your kidneys are regulating potassium excretion properly and that intake and losses are balanced. Your heart rhythm and muscle function are supported by an appropriate intracellular-to-extracellular potassium gradient.

High

High potassium (hyperkalaemia) can cause dangerous heart rhythm abnormalities (arrhythmias) and muscle weakness. Common causes include kidney failure (reduced excretion), excessive potassium supplementation, medications such as ACE inhibitors or potassium-sparing diuretics, cell breakdown (rhabdomyolysis, haemolysis), and Addison's disease.

Low

Low potassium (hypokalaemia) causes muscle weakness, cramps, constipation, and potentially fatal cardiac arrhythmias. Common causes include diuretic use, vomiting, diarrhoea, excessive sweating, inadequate dietary intake, and conditions such as hyperaldosteronism.

Frequently Asked Questions

What causes low potassium? expand_more
The most common causes are diuretic medications (water pills), vomiting, diarrhoea, poor dietary intake, excessive sweating, and certain conditions such as Cushing's syndrome or hyperaldosteronism. Low magnesium can also make hypokalaemia difficult to correct.
What causes high potassium? expand_more
High potassium is most often seen in kidney disease (impaired excretion), with ACE inhibitor or potassium-sparing diuretic use, after significant tissue injury, or in adrenal insufficiency (Addison's disease). It can also be falsely elevated due to haemolysis in the blood sample.
What is the normal potassium level? expand_more
Normal potassium is 3.5 to 5.1 mmol/L. Values below 3.5 mmol/L are hypokalaemia; above 5.1 mmol/L is hyperkalaemia. Levels below 2.5 or above 6.0 mmol/L are medical emergencies requiring immediate treatment.
Which foods are high in potassium? expand_more
High-potassium foods include bananas, oranges, potatoes, sweet potatoes, avocados, spinach, tomatoes, lentils, and dairy products. If you have kidney disease, your doctor may advise limiting these foods to prevent hyperkalaemia.
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