In short
A potassium above 5.5 mmol/L can affect heart rhythm, yet it often causes no symptoms at all. A surprisingly large share of high readings are artefacts of how the blood was drawn — here's how the two are told apart.
Emergency if: A potassium of 6.5 mmol/L or above, or any raised potassium together with palpitations, marked muscle weakness, chest pain or fainting — go to emergency care now.
On your report
Potassium, Creatinine, eGFR (Estimated Glomerular Filtration Rate), Urea / BUN +2 more
On this page
01
The Numbers
Potassium normally sits somewhere in the range of about 3.5 to 5.2 mmol/L, and the exact cut-offs printed on your report vary between laboratories. Above roughly 5.5 is hyperkalemia, and a value of 6.5 or more is treated as a medical emergency whether or not the person feels unwell.
Potassium matters far out of proportion to how little of it circulates: it sets the electrical charge across cell membranes, so heart and muscle cells are exquisitely sensitive to a shift of even a fraction of a millimole.
02
First Question: Is the Result Real?
Potassium sits mostly inside cells, so anything that damages red cells in the tube pushes the measured value up falsely. A difficult draw, a fine needle, clenching the fist repeatedly, a tourniquet left on too long, shaking the sample, a delay before processing, or a very high platelet or white cell count can all do it.
That is why an unexpectedly high potassium in someone who feels perfectly well, with normal kidney function and no relevant medicines, is often repeated first rather than treated. A carefully taken repeat sample resolves a good number of these results — but the repeat should be done promptly, not skipped.
03
When It Is Genuinely High
Reduced kidney function is the usual reason — the kidneys are the main route out of the body for potassium. Medicines are the other big one: ACE inhibitors, angiotensin receptor blockers, spironolactone and amiloride, along with anti-inflammatory painkillers and trimethoprim, all reduce potassium excretion.
Less obvious sources include potassium supplements and the reduced-sodium salt substitutes sold as a heart-healthy swap, which are largely potassium chloride. Uncontrolled diabetes, Addison's disease and any large breakdown of tissue — a crush injury, severe burns, rhabdomyolysis — also push potassium out of cells into the blood.
04
What It Feels Like, and What Is Done
Often nothing, which is precisely the danger. When symptoms do appear they are vague — muscle weakness, tingling, nausea, tiredness — or sudden and serious: palpitations, fainting, or a dangerous heart rhythm. An ECG is done quickly because the electrical changes it shows guide how urgently to act.
Hospital treatment stabilises the heart with intravenous calcium, then drives potassium back into cells with insulin and glucose and a nebulised reliever inhaler. Potassium binders taken by mouth remove it from the body over hours, and dialysis is used when the kidneys cannot cope.
05
Living With a Tendency to Run High
If you have kidney disease, a dietitian's advice is more useful than a generic list — but the usual high-potassium foods are bananas, potatoes, tomatoes and tomato purée, oranges and orange juice, dried fruit, nuts, beans, chocolate and coconut water. Checking labels on salt substitutes is a small change with an outsized effect.
Do not stop an ACE inhibitor, receptor blocker or spironolactone on your own because of one result. These drugs protect the heart and kidneys, and the usual approach is a dose adjustment with monitoring rather than stopping — a decision that belongs with the prescriber.
When to act
Emergency — act now
A potassium of 6.5 mmol/L or above, or any raised potassium together with palpitations, marked muscle weakness, chest pain or fainting — go to emergency care now.
Same-day — call promptly
A potassium between 5.5 and 6.4, or any raised value in someone with kidney disease or taking an ACE inhibitor, receptor blocker or spironolactone — contact the prescriber today.
Routine — see a doctor
A mildly raised value in a well person after a difficult blood draw — arrange a properly taken repeat test rather than assuming it was a laboratory error.
Values mentioned in this story
Each one opens a visual guide with its normal range and what moves it — upload a report and we place your own numbers on the same scale.
Sources
- High potassium level — MedlinePlus Medical Encyclopediamedlineplus.gov
- Potassium — MedlinePlusmedlineplus.gov
- Potassium test — MedlinePlus Medical Encyclopediamedlineplus.gov
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