Hyperkalemia (High Potassium)

Why potassium matters

About 98% of the body's potassium is inside cells. The difference between potassium inside and outside cells sets the electrical charge that lets nerves and muscles fire. Small changes in blood potassium alter this charge. High potassium makes heart cells more excitable at first, then less able to conduct electricity, which can lead to dangerous rhythms or cardiac arrest.

The kidneys remove about 90% of potassium from the diet. Insulin and adrenaline move potassium into cells.

Causes

Reduced removal by the kidneys

• Chronic kidney disease, especially advanced stages
• Acute kidney injury from dehydration, infection or medicines
• Medicines that reduce kidney potassium excretion: - ACE inhibitors and ARBs - spironolactone, eplerenone, amiloride, triamterene - NSAIDs - trimethoprim (an antibiotic) - heparin - calcineurin inhibitors (tacrolimus, cyclosporine)
• Addison's disease and low aldosterone states
• Type 4 renal tubular acidosis, common in diabetes

Potassium shifting out of cells

• Diabetic ketoacidosis and very high blood sugar from lack of insulin
• Acidosis
• Cell breakdown: rhabdomyolysis, severe burns, crush injuries, tumor lysis syndrome, internal bleeding
• Medicines: beta-blockers, digoxin toxicity, succinylcholine

Too much intake

Rarely the sole cause, but contributes in people with kidney problems:

• potassium supplements
• salt substitutes containing potassium chloride
• high-potassium foods in advanced kidney disease

False results (pseudohyperkalemia)

If red blood cells break during or after the blood draw (hemolysis), potassium leaks out and the result is falsely high. Tight tourniquets, fist clenching, delays in processing and very high white cell or platelet counts can do this. An unexpected high result is usually repeated promptly.

Symptoms

Many people have no symptoms until levels are high. Possible symptoms:

• muscle weakness or heaviness, especially in the legs
• tingling or numbness
• tiredness
• nausea
• palpitations or an irregular heartbeat
• shortness of breath
• in severe cases, paralysis, collapse or cardiac arrest

Diagnosis

• Blood test: serum potassium; repeated if a false result is possible.
• ECG: shows the effect on the heart. Changes include tall, peaked T waves, flattened P waves, widened QRS complexes and, in extreme cases, a sine-wave pattern. A normal ECG does not rule out danger.
• Further tests: kidney function, blood sugar, blood gas for acidosis, creatine kinase, and sometimes cortisol and aldosterone.
• Medicine review.

Treatment

Emergency treatment of severe hyperkalemia

1. Protect the heart: intravenous calcium stabilizes heart cell membranes within minutes. It does not lower potassium.
2. Shift potassium into cells: intravenous insulin with glucose, and inhaled salbutamol (albuterol). These work within 15 to 30 minutes and last a few hours. Blood sugar is monitored to prevent hypoglycemia.
3. Remove potassium from the body: - potassium binders taken by mouth (such as sodium zirconium cyclosilicate or patiromer) - diuretics if the kidneys are working - dialysis for severe cases, kidney failure, or when other measures fail
4. Treat the cause: stop contributing medicines, treat DKA, rehydrate, manage rhabdomyolysis.

Chronic or mild hyperkalemia

• review and adjust medicines; potassium binders may allow people with heart or kidney disease to continue beneficial ACE inhibitors, ARBs or spironolactone
• low-potassium diet guided by a dietitian for people with advanced kidney disease
• avoid potassium-containing salt substitutes and supplements unless prescribed
• avoid NSAIDs
• treat acidosis and control blood sugar
• regular blood tests

Foods high in potassium

For people advised to limit potassium (mostly those with advanced kidney disease), common high-potassium foods include bananas, oranges and orange juice, potatoes and sweet potatoes, tomatoes and tomato sauce, dried fruit, beans and lentils, avocado, spinach, and salt substitutes. Cooking methods such as boiling and draining vegetables reduce potassium. Do not restrict potassium unless your clinician advises it.

Prevention

• blood tests after starting or changing ACE inhibitors, ARBs or spironolactone
• "sick day rules": during vomiting, diarrhea or dehydration, some medicines may need to be paused temporarily; ask your doctor or pharmacist
• keep dialysis appointments
• check with a pharmacist before using salt substitutes or supplements

Frequently asked questions

What level of potassium is dangerous?

A potassium level of 6.5 mmol/L or higher is considered severe and needs emergency treatment, as is any raised level with ECG changes. Levels of 6.0 to 6.4 need urgent same-day assessment. Mildly raised levels, 5.5 to 5.9, need a repeat test and medicine review.

What are the symptoms of high potassium?

High potassium often causes no symptoms. When it does, people may notice muscle weakness, tiredness, tingling, nausea, palpitations or an irregular heartbeat. Severe hyperkalemia can cause paralysis and cardiac arrest, which is why it is checked with an ECG.

What causes high potassium?

The most common causes are kidney disease and medicines such as ACE inhibitors, ARBs, spironolactone, NSAIDs and trimethoprim. Others include uncontrolled diabetes, Addison's disease, tissue breakdown from injury or rhabdomyolysis, and excess potassium supplements or salt substitutes.

Can dehydration cause high potassium?

Dehydration can contribute by reducing kidney function, especially in people taking ACE inhibitors, ARBs, diuretics or NSAIDs. This is why some medicines may be paused during vomiting or diarrhea under medical advice.

Can a high potassium blood test be wrong?

Yes. If red blood cells break during or after the blood draw, potassium leaks out and gives a falsely high reading. Doctors often repeat an unexpectedly high result, but they treat high levels with ECG changes as real until proven otherwise.