High potassium (hyperkalaemia): causes, risks and treatment in the UK

Potassium is a mineral that, according to the NHS, helps control the balance of fluids in the body and helps the heart muscle work properly. The NHS says potassium is found in most types of food and that you should be able to get all you need from a varied, balanced diet.

Hyperkalaemia is the medical term for a raised potassium level in the blood. The BNF grades it as mild, moderate or severe according to the serum potassium concentration, in mmol/litre, as shown in the table below. It is identified from a blood test, and the BNF says the clinical condition, ECG and rate of potassium rise are considered alongside the number.

The BNF says people most at risk of hyperkalaemia include those with chronic kidney disease (CKD), heart failure and diabetes. Because the kidneys are the main route by which potassium leaves the body, reduced kidney function is a central factor. NICE Clinical Knowledge Summaries lists hyperkalaemia among the complications of acute kidney injury.

Some medicines increase serum potassium. The BNF lists ACE inhibitors, angiotensin-II receptor antagonists, mineralocorticoid receptor antagonists, potassium-sparing diuretics, NSAIDs, non-selective beta-blockers and trimethoprim. The NHS adds that older people may be more at risk of harm from potassium supplements because their kidneys may be less able to remove potassium from the blood, and should not take potassium supplements unless advised by a doctor.

Other contributors the BNF says should be managed include constipation, acidosis and poorly controlled diabetes. These are non-dietary causes and are addressed before dietary restriction.

The BNF says severe hyperkalaemia can lead to life-threatening cardiac arrhythmias and cardiac arrest, which is why it requires urgent hospital assessment. A heart tracing (ECG) is part of the assessment, and the BNF says hyperkalaemia in the presence of ECG changes calls for urgent treatment to temporarily protect against excitability of the heart muscle.

The BNF also says that people with persistent hyperkalaemia need monitoring of serum potassium concentrations, and that the UK Kidney Association publishes detailed guidance for clinicians on managing it in adults.

The BNF says that interventions to lower serum potassium should be started when it is 5.5 mmol/litre or more, and that mild or moderate cases found in the community can usually be managed without admission, unless the person is acutely unwell or has acute kidney injury. For moderate hyperkalaemia, the clinical condition, ECG and rate of potassium rise are considered, and treatment may follow the severe pathway if needed.

Steps described in the BNF include:

• Reviewing and managing drugs that exacerbate hyperkalaemia, weighing both the risks and benefits of each.

• Treating non-dietary causes such as constipation, acidosis and poorly controlled diabetes.

• Dietary advice from a renal dietitian for people with CKD and persistent hyperkalaemia.

• For people with CKD and low bicarbonate, sodium bicarbonate, which also treats metabolic acidosis.

• A loop diuretic, in selected people who are passing urine and are not dehydrated.

• Potassium-binding medicines started by specialists, such as sodium zirconium cyclosilicate or patiromer calcium, for people who otherwise cannot take an optimised dose of RAAS inhibitors, or cannot take them at all, because of hyperkalaemia.

Severe hyperkalaemia is treated in hospital. The BNF describes an urgent approach with several parts: drugs that raise potassium are reviewed and withheld; intravenous calcium (calcium gluconate is preferred, except in cardiac arrest where calcium chloride is preferred) protects the heart if there are ECG changes; an intravenous insulin and glucose infusion moves potassium into cells, lowering the level within 15 minutes with the peak effect at 30 to 60 minutes; and nebulised salbutamol has an additive effect.

To remove potassium from the body, the BNF recommends sodium zirconium cyclosilicate or patiromer calcium in the emergency management of severe hyperkalaemia, and says some people may need haemodialysis. The infusion can be repeated if the level does not fall below 6 mmol/litre within 2 hours or if it rebounds, and specialist advice is sought if potassium stays uncontrolled.

NICE technology appraisal TA623 recommends patiromer as an option in emergency care for acute life-threatening hyperkalaemia alongside standard care, and for some people with persistent hyperkalaemia, stages 3b to 5 CKD or heart failure, who have a confirmed serum potassium of at least 6.0 mmol/litre and cannot take, or are taking a reduced dose of, a RAAS inhibitor because of hyperkalaemia.

Prevention rests on kidney and medicine review. This can include monitoring the potassium level, avoiding potassium supplements unless a doctor advises them (the NHS says older people in particular should not take them without advice), looking for constipation and acidosis, and discussing with the prescriber whether the dose of a RAAS inhibitor can be maintained with the help of a potassium binder or a dietitian's advice.

NICE explains in TA623 that patiromer may allow people to stay on RAAS inhibitors, medicines used to treat heart failure and kidney disease, for longer or at a higher dose, which may extend life and improve quality of life. Never stop a prescribed medicine yourself because of a high potassium result; ask your GP, pharmacist or kidney team what to do first.

On the NHS, hyperkalaemia is usually picked up on routine bloods by a GP or hospital team and managed through medicines review, with a kidney specialist involved when it is persistent or severe. Private routes can speed up blood tests and specialist review, but severe hyperkalaemia is an emergency that needs hospital treatment whichever route you use. If you are given a result and do not understand what to do, ask for the repeat test date and who is responsible for your medicines review.