Intended for healthcare professionals

Practice Rational Testing

Investigating hyperkalaemia in adults

BMJ 2015; 351 doi: (Published 20 October 2015) Cite this as: BMJ 2015;351:h4762
  1. Timothy J McDonald, principal clinical scientist and honorary clinical senior lecturer12,
  2. Richard A Oram, specialist registrar23,
  3. Bijay Vaidya, consultant endocrinologist and honorary associate professor4
  1. 1Department of Blood Sciences, Royal Devon and Exeter Hospital, Exeter EX2 5DW, UK
  2. 2NIHR Exeter Clinical Research Facility, University of Exeter Medical School, Exeter
  3. 3Department of Renal Medicine, Royal Devon and Exeter Hospital, Exeter
  4. 4Department of Endocrinology, Royal Devon and Exeter Hospital and University of Exeter Medical School, Exeter
  1. Correspondence to: B Vaidya b.vaidya{at}

The bottom line

  • The cause of hyperkalaemia in adults is usually obvious from the patient’s history: the commonest causes are acute kidney injury, chronic kidney disease, and drugs

  • Spurious hyperkalaemia is a common cause of raised serum potassium levels and must be excluded when investigating hyperkalaemia of uncertain aetiology

  • Severe hyperkalaemia (>6.5 mmol/L) is associated with life threatening arrhythmias and should be treated in an acute facility with electrocardiographic monitoring

  • If hyperkalaemia is moderate or severe, or its cause unclear, initial investigations are electrocardiography, renal function, glucose, full blood count, and assessment of acid-base balance

  • Refer patients with no obvious explanation for their hyperkalaemia for endocrine or renal assessment

A 42 year old woman was admitted to hospital after a blood test performed by her general practitioner for investigation of intermittent abdominal pain showed a high serum potassium level of 6.6 mmol/L (reference range 3.5-5.3 mmol/L).1 She was otherwise well and not taking any medications. When she arrived in the emergency medical unit, her blood pressure was 140/70 mmHg, and other physical examination showed no significant abnormalities. Her electrocardiographic (ECG) results were normal.

What is the next investigation?


Hyperkalaemia is defined as serum potassium concentration >5.3 mmol/L and is commonly graded as mild (5.4-6.0 mmol/L), moderate (6.1-6.5 mmol/L) or severe (>6.5 mmol/L).2 It is reported in 1-2.5% of hospitalised patients,3 and in 0.2-0.7% of a population based cohort of people aged ≥55 years.4 It is most often associated with renal failure and drugs that cause hyperkalaemia.3

Most potassium (98%) in the body is intracellular, with a small proportion in the extracellular compartment.5 This intracellular-extracellular potassium gradient is essential for normal nerve and muscle function. Small increases in extracellular potassium can have adverse effects on the heart and skeletal muscles. Mild hyperkalaemia is often asymptomatic, but severe hyperkalaemia is associated with life threatening …

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