Hyperkalaemia (High Potassium): A Case-Based Guide

The case: a routine blood test surprise

In our teaching scenario, a woman in her seventies with long-term kidney disease feels tired, weak and slightly nauseous. She has recently started a new blood pressure tablet and has been eating more bananas and low-salt substitute, which is often high in potassium. A routine blood test at her GP surgery shows a markedly raised potassium level. The surgery contacts her urgently and arranges hospital assessment. She has few symptoms, which is common: hyperkalaemia is often silent until it becomes severe. This case shows why blood tests matter for people on certain medicines or with kidney problems, and how a hidden change in body chemistry can pose a serious risk.

What potassium does and why balance matters

Potassium is a mineral that helps nerves and muscles work, including the heart muscle. The body keeps blood potassium within a narrow range, mostly by removing extra amounts through the kidneys. When kidneys are not working well, or when certain medicines reduce potassium removal, levels can climb. Too much potassium changes the electrical signals that make the heart beat steadily. Mild rises may cause no symptoms or vague tiredness and muscle weakness. Higher levels can lead to a dangerously slow, fast or irregular heartbeat and, at the extreme, cardiac arrest. Because symptoms are unreliable, the level is measured by a blood test, and a heart tracing (ECG) helps show whether the heart is being affected.

Common causes and contributors

Several factors often combine to raise potassium. Reduced kidney function is the most important, because the kidneys normally clear the excess. Some widely used medicines can raise potassium, including certain blood pressure and heart tablets and some water tablets that spare potassium. Dehydration, uncontrolled diabetes, and tissue injury can also contribute. Diet plays a part too: potassium-rich foods and, importantly, low-sodium salt substitutes that replace sodium with potassium can tip a vulnerable person over the edge. Sometimes a high reading is falsely raised because the blood sample clotted or was handled poorly, so an unexpected result is often repeated. Identifying and removing the contributing causes is a central part of treatment.

Emergency management in hospital

When potassium is dangerously high, or the ECG shows changes, treatment is urgent and follows a clear order. The heart is protected first with a medicine that stabilises its electrical activity. Next, other treatments temporarily move potassium out of the blood and into cells to buy time. Finally, the body is helped to remove the excess potassium altogether. Offending medicines are paused, fluids and diet are reviewed, and the underlying cause is treated. In severe cases, or when the kidneys cannot cope, dialysis may be needed to filter the blood. Potassium is rechecked frequently, and the person is monitored on a heart trace. Clinicians choose all doses individually; this article names none.

Recovery and preventing it happening again

Once potassium is safely lowered and the cause addressed, most people recover well. Prevention focuses on the factors that can be controlled. People at risk, such as those with kidney disease or on certain heart and blood pressure medicines, should attend blood test appointments as advised. They should avoid low-sodium salt substitutes unless told they are safe, and follow any dietary guidance about high-potassium foods. Staying hydrated, especially during illness with vomiting or diarrhoea, helps the kidneys work. Never stop or change prescribed medicines without advice, but do ask your GP or pharmacist to review them if you are worried. Wearing details of your conditions and taking a current medicines list to appointments also helps keep you safe.