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Doctor's Assessment Included

Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

Minerals

Potassium levels: what do they tell you about your electrolyte balance?

Potassium is lost through sweat and is critical for muscle contraction and heart function during exercise. Monitoring helps prevent cramping and maintain performance.

Reference Ranges

Male
mmol/l
Low 3.5 Normal 5 High
Female
mmol/l
Low 3.5 Normal 5 High

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

What It Measures

This test measures the potassium concentration in your blood, expressed in millimoles per litre (mmol/L). The normal range is 3.5–5.0 mmol/L and is the same for men and women. Most of the potassium in your body (98%) is inside cells; only a small portion circulates in the blood. This makes the blood value sensitive to disruption.

The kidneys are the primary regulators of your potassium balance. With reduced kidney function, potassium can accumulate in the blood (hyperkalaemia). Conversely, excessive fluid loss (vomiting, diarrhoea, diuretic use) can lead to potassium deficiency (hypokalaemia).

Why It Matters

Potassium is directly linked to the electrical conductivity of the heart. Both too high and too low potassium can cause heart rhythm disorders that in severe cases can be life-threatening. This makes potassium one of the most critical blood values.

With certain medications, potassium monitoring is essential. ACE inhibitors and ARBs (commonly used blood pressure medications) can raise potassium. Diuretics such as furosemide and hydrochlorothiazide lower potassium. With combined use, periodic monitoring is necessary.

When to Test

Potassium is routinely measured during kidney function monitoring, with blood pressure medication (ACE inhibitors, ARBs, diuretics), and for symptoms such as muscle cramps, muscle weakness, palpitations, or unexplained fatigue. With severe diarrhoea or vomiting, monitoring is also sensible due to the risk of potassium loss. Fasting is not required.

Symptoms

Low Levels

Low potassium (below 3.5 mmol/L, hypokalaemia) causes muscle cramps, muscle weakness, fatigue, constipation, and palpitations. In severe deficiency (below 2.5 mmol/L), life-threatening heart rhythm disorders and muscle paralysis can occur. Common causes are diuretic use, excessive vomiting or diarrhoea, and insufficient dietary intake.

High Levels

High potassium (above 5.0 mmol/L, hyperkalaemia) can manifest as muscle cramps, tingling, muscle weakness, and heart rhythm disorders. At values above 6.0 mmol/L, there is risk of serious cardiac conduction disorders. The most common causes are reduced kidney function, ACE inhibitors/ARBs, excessive potassium supplementation, and tissue damage. Note: a falsely elevated potassium can occur if the blood sample is stored too long or if collection was difficult (haemolysis).

Lifestyle Tips

Potassium is found in many foods: bananas, potatoes, spinach, avocado, beans, nuts, and dairy products. Most people get sufficient potassium through a varied diet. With diuretic use, extra attention to potassium-rich foods may be needed. Only use potassium supplements on medical advice — too much can be just as dangerous as too little. Adequate hydration supports potassium regulation by the kidneys.

Frequently Asked Questions

What is a normal potassium level?
Normal values are between 3.5 and 5.0 mmol/L. Values below 3.5 (hypokalaemia) or above 5.0 (hyperkalaemia) require attention, as potassium abnormalities can directly affect the heart.
Can I get too much potassium from food?
With healthy kidneys, excess potassium from food is almost never a problem — the kidneys excrete surplus potassium. With reduced kidney function, potassium levels can become too high from potassium-rich food or supplements.
Which medications affect potassium?
ACE inhibitors, ARBs, and potassium-sparing diuretics can raise potassium. Loop diuretics (furosemide) and thiazide diuretics lower potassium. Periodic potassium monitoring is standard when using these medications.
Do I need to fast before a potassium test?
No, fasting is not required. However, it is important that the blood sample is processed quickly, as a sample stored for too long or damaged can give a falsely elevated potassium.
Can dehydration affect my potassium?
Yes, severe dehydration can raise blood potassium levels because blood volume decreases. Conversely, excessive fluid loss from vomiting or diarrhoea can lead to potassium deficiency. Adequate hydration is important for a stable potassium balance.
When is abnormal potassium dangerous?
A potassium below 2.5 mmol/L or above 6.0 mmol/L is considered potentially dangerous due to the risk of heart rhythm disorders. This requires immediate medical assessment and possibly treatment.