GPAtlas🧭 When to suspect
Hyperkalaemia is most often a laboratory finding rather than a clinical one – there is no single agreed definition, but UK guidance treats a serum potassium > 5.5 mmol/L as the threshold for action. The majority of cases are asymptomatic and picked up on routine or drug-monitoring bloods. When symptoms occur they are non-specific: muscle weakness, paraesthesia, palpitations, or general malaise.
The danger is that severe hyperkalaemia can precipitate fatal arrhythmia or cardiac arrest with little warning. The two primary-care skills are therefore to confirm the result is genuine (artefactual rises are common), then risk-stratify by the potassium level. Management is driven almost entirely by the number and the clinical context.
Suspect and actively monitor in patients with chronic kidney disease (CKD), diabetes, heart failure, acute kidney injury (AKI), or Addison's disease, and in anyone taking a drug that raises potassium – particularly renin–angiotensin–aldosterone system inhibitors (RAASi): angiotensin-converting enzyme inhibitors (ACE inhibitors), angiotensin receptor blockers (ARBs) and mineralocorticoid receptor antagonists (MRAs).
| Serum potassium | Classification | Action |
|---|---|---|
| ≤ 5.5 mmol/L | Within reference range | No action if well; routine monitoring per risk |
| 5.5–5.9 mmol/L | Mild | Address reversible causes; repeat within ~1 week |
| 6.0–6.4 mmol/L | Moderate | Usually managed in community if well: ECG, treat causes, repeat within 1 day |
| ≥ 6.5 mmol/L | Severe | Immediate admission regardless of symptoms or ECG |
Source: UK Kidney Association (2023) · NICE TA1148
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