Of all the minerals in your blood, potassium has the smallest room to move. The normal range sits roughly between 3.5 and 5.0 mmol/l. That is a margin of one and a half. Outside it, your heart rhythm starts to notice.
The short version: a low potassium usually comes from loss, not from your diet. Diuretics, vomiting and diarrhoea are the usual suspects. A high potassium often points to your kidneys, to medication, or, and this is rarely mentioned, to the blood draw itself.
That last one is the most interesting part of this topic, so I will come back to it below.
What is a normal potassium value?
Most Dutch laboratories use roughly 3.5 to 5.0 mmol/l as the reference for serum potassium. Below 3.5 is called hypokalaemia, above 5.0 hyperkalaemia. Those cut-offs differ slightly per lab, so always read the reference range printed on your own result.
Why the band is so narrow becomes clear once you see where potassium sits. Around 98 percent of your potassium is inside your cells and only 2 percent in your blood. Your body guards that small portion closely, because the difference between inside and outside the cell is what makes electrical signals possible (Palmer 2016, PMID 27756725).
That mechanism explains why potassium touches both your muscles and your heart. Nerves and heart cells lean on that voltage difference.
What does a low potassium value mean?
A low potassium almost always means you are losing it somewhere. Through your kidneys on diuretics, through your gut with diarrhoea, or through vomiting. Simply eating too little potassium is a rare cause here, because potassium is in nearly everything: potatoes, bananas, pulses, vegetables.
The complaints are unspecific. Muscle weakness, cramp, fatigue and constipation are the most common. At markedly low values, heart rhythm disturbances can develop, which is why doctors take this value seriously (Kardalas 2018, PMID 29540487).
| Possible cause | How it lowers potassium |
|---|---|
| Diuretics | Your kidneys excrete more potassium |
| Vomiting or diarrhoea | Direct loss through stomach and gut |
| Laxatives | Loss through the gut with prolonged use |
| Excessive liquorice | Affects the hormonal regulation of potassium |
| Low intake | Rare on its own, usually in combination |
Imagine two people with a potassium of 3.3 mmol/l. One recently started a diuretic for high blood pressure; the other takes nothing and simply cleared their plate. In the first, the result is explained. In the second, a question is still open. Same number, different story.
What does a high potassium value mean?
A high potassium often points to your kidneys, since they control excretion. Reduced kidney function, certain blood pressure drugs and potassium-sparing diuretics are the usual causes. Significant tissue breakdown, for instance after a hard training session, can also lift the value temporarily.
There is another cause that has nothing to do with your body, and you rarely see it named on other sites. If red blood cells are damaged during the draw, potassium leaks out of them into the serum. The result then reads too high while nothing is wrong. This is called haemolysis, and it is a well known pre-analytical source of error in potassium testing (Schlueter 2023, PMID 37042478).
A tourniquet pulled too tight, a needle too thin, or a tube left standing too long can be enough. That is why a second draw after an unexpectedly high result is so often the first step, rather than a drug.
My advice stays simple: do not panic over a single high value without symptoms. Ask first whether the sample was haemolysed.
How are potassium and salt connected?
Potassium and sodium act as counterweights. Potassium sits mainly in unprocessed plant foods, sodium mainly in processed food and salt. The Dutch Voedingscentrum therefore points out that many people in the Netherlands take in relatively much sodium and relatively little potassium.
That ratio is more interesting than either number alone. More vegetables and pulses shift the balance the other way by themselves. There is more on this in salt and your blood values and in low sodium explained.
When do you have your potassium measured?
Measuring is mainly useful when there is a reason. If you take diuretics or blood pressure medication, if you have had prolonged vomiting or diarrhoea, or if you notice palpitations and muscle weakness, a potassium value gives direction. Without symptoms and without medication, a stand-alone measurement usually adds little.
Potassium is almost always read together with sodium and kidney values, because those three explain each other. You can have potassium measured on its own or as part of an extended health checkup at Vitalcheck, without a referral.
For how potassium fits the wider picture, read the pillar on minerals and trace elements. To understand why your kidneys are so central here, read kidney function explained. Always discuss an abnormal result with your GP before changing anything.
References
- Kardalas E, et al. Hypokalemia: a clinical update. Endocr Connect. 2018. PMID 29540487.
- Palmer BF, Clegg DJ. Physiology and pathophysiology of potassium homeostasis. Adv Physiol Educ. 2016. PMID 27756725.
- Schlueter K, et al. Erroneous potassium results: preanalytical causes, detection and corrective actions. Crit Rev Clin Lab Sci. 2023. PMID 37042478.
- Voedingscentrum. Potassium.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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