Conditions · Metabolism (biochemistry)
Hyperkalaemia !
Blood potassium is high, mainly from kidney failure or drugs; it can stop the heart and is an emergency.
Updated 2026-11-01
Structures involved
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- Kidneys
- Left adrenal gland
- Right adrenal gland
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Bundle branches
In physiology
- The ventricular action potential
- ECG basics: waves, intervals and leads
- The ECG in potassium and calcium disorders
- Body fluid compartments
- The resting membrane potential
- The Nernst and Goldman equations
- Ion channels and gating
- The HPA axis and its circadian rhythm
- Aldosterone: actions and control
- Skeletal, cardiac and smooth muscle compared
- Refractory periods and excitability
- Distal tubule and collecting duct
- Potassium balance
- Reasoning through fluid and electrolyte imbalances
- Where and how diuretics act
- Renal handling of H⁺ and bicarbonate
- Physiology of acute and chronic kidney failure
What it is
A high serum potassium from reduced renal excretion, potassium leaving cells or excess intake; the cause of death is arrhythmia.
Who gets it
It is common in chronic kidney disease, especially with drugs that block the renin–angiotensin–aldosterone system, and in acute kidney injury.
Causes
- Reduced excretion: acute kidney injury, advanced chronic kidney disease, hypoaldosteronism (adrenal insufficiency, RTA type 4)
- Drugs: ACE inhibitors, ARBs, spironolactone, amiloride, trimethoprim, NSAIDs, heparin, calcineurin inhibitors
- Shift out of cells: acidosis, insulin lack (ketoacidosis), tumour lysis, rhabdomyolysis, haemolysis, β-blockers, digoxin overdose, succinylcholine
- Intake: supplements, potassium salt substitutes, massive transfusion
- Pseudohyperkalaemia: haemolysed sample, prolonged tourniquet, extreme leukocytosis or thrombocytosis
Risk factors
- Chronic kidney disease
- Diabetes
- ACE inhibitor or ARB combined with spironolactone
- Chemotherapy of high-burden tumours (tumour lysis)
- Crush injury
Pathophysiology
As extracellular potassium rises, the resting potential becomes less negative; excitability first increases and then sodium channels inactivate, so conduction slows. The ECG shows peaked T waves, then a long PR and loss of the P wave, wide QRS, a sine-wave pattern and ventricular fibrillation or asystole. In skeletal muscle it causes ascending weakness and paralysis. The kidney excretes potassium in the collecting duct under aldosterone and according to distal sodium delivery, which is why kidney failure and aldosterone blockade cause it.
Classification
- By severity per the laboratory and, above all, by ECG changes
- Acute or chronic
- True or pseudohyperkalaemia
Symptoms and signs
- Often silent until an arrhythmia occurs
- Muscle weakness, paraesthesia
- Palpitations
- Bradycardia
- Flaccid paralysis when severe
Diagnosis
- Clinical
- Review drugs, kidney function, diabetes and causes of cell breakdown; rule out pseudohyperkalaemia before treating if the ECG is normal.
- Tests
- Serum potassium (repeated without haemolysis), immediate ECG, creatinine and BUN, gases (acidosis), glucose, CK, uric acid and LDH (tumour lysis), cortisol and aldosterone if adrenal insufficiency is suspected.
- Imaging
- Renal ultrasound if urinary obstruction is suspected as a cause of kidney injury.
Treatment
- Acute
- Stabilise the cardiac membrane with intravenous calcium when the ECG is abnormal
- Acute
- Shift potassium into cells: insulin with glucose, nebulised β2 agonists; bicarbonate if acidotic
- Medical
- Remove potassium from the body: loop diuretics if passing urine, gut binders or resins; stop causative drugs
- Procedure
- Haemodialysis in kidney failure, refractory hyperkalaemia or massive cell breakdown
- Follow-up
- Continuous cardiac monitoring and serial potassium (insulin and β2 agonists only buy time)
Complications
- Ventricular fibrillation and asystole
- Paralysis
- Sudden death
Prognosis
Severe hyperkalaemia carries high mortality if not treated in time; it responds well to prompt treatment and correction of the cause.
Prevention
- Checking potassium and creatinine when starting or raising ACE inhibitors, ARBs or spironolactone
- Hydration and tumour lysis prophylaxis before chemotherapy
- Avoiding potassium salt substitutes in kidney disease
Test yourself
Think of the answer, then tap the question to see it.
What is the first ECG change in hyperkalaemia?
Tall, peaked T waves; then PR and QRS lengthen, and it can progress to ventricular fibrillation or asystole.
Why is intravenous calcium given in hyperkalaemia with ECG changes?
It stabilises the myocardial membrane and protects against arrhythmia, although it does not lower potassium.
What is pseudohyperkalaemia?
A falsely high potassium because it leaks from cells in the sample: haemolysis, prolonged tourniquet or very high white cells or platelets.
Why can spironolactone cause hyperkalaemia?
It blocks aldosterone, the main signal for the collecting duct to secrete potassium.
Related conditions
- Hypokalaemia
- Acute kidney injury
- Chronic kidney disease
- Tumour lysis syndrome
- Adrenal insufficiency
- Diabetic ketoacidosis
Educational information, not medical advice. For any symptom, see a health professional.
Sources: High potassium level: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Potassium Blood Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Potassium test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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