Potassium Blood Test: Hyperkalaemia, Hypokalaemia and Pseudo-Hyperkalaemia Explained
Potassium > 6.5 is a medical emergency. Learn ECG changes, spurious elevation, and safe correction.
Normal potassium is 3.5–5.0 mmol/L. Above 6.5 mmol/L or any level with ECG changes is a medical emergency. Rule out pseudo-hyperkalaemia (haemolysis, delayed processing, tight tourniquet) with a repeat sample. Treatment sequence: calcium gluconate → insulin + glucose → salbutamol → definitive removal (dialysis or new binders).
Hyperkalaemia is the electrolyte disturbance with the highest immediate mortality risk. The 2023 UK Renal Association / RA guideline defines severe hyperkalaemia as ≥ 6.5 mmol/L or ≥ 6.0 with ECG changes; treatment must not wait for the confirmatory sample. ECG changes progress: tall tented T waves → PR prolongation → wide QRS → sine-wave → asystole. Standard emergency sequence: (1) IV calcium gluconate 10% 10 mL to stabilise myocardium (does not lower potassium); (2) insulin 10 units in 25 g glucose IV to shift potassium intracellularly; (3) nebulised salbutamol 10–20 mg for additive shift; (4) definitive removal — dialysis for oliguric AKI, patiromer or sodium zirconium cyclosilicate for chronic RAAS-inhibitor-associated hyperkalaemia. Pseudo-hyperkalaemia (haemolysis, delayed lab processing, thrombocytosis, tight tourniquet) is common — always repeat if borderline and unexpected. Hypokalaemia (< 3.5) is usually GI losses, diuretics, or hyperaldosteronism; check magnesium (low Mg blocks potassium repletion) and correct together.
- Normal K+
- 3.5 – 5.0 mmol/L
- Emergency
- ≥ 6.5 or ECG changes
- First drug
- Calcium gluconate (myocardial stabilisation)
- Shifter
- Insulin 10 U + 25 g glucose
- Remover
- Dialysis, patiromer, sodium zirconium cyclosilicate
Hyperkalaemia severity + management
| K+ (mmol/L) | Severity | Action |
|---|---|---|
| 5.1 – 5.9 | Mild | Review K+ intake, drugs; recheck. |
| 6.0 – 6.4 | Moderate | ECG. Stop offenders. Insulin + glucose if ECG changes. |
| ≥ 6.5 | Severe | Emergency. Full sequence: Ca → insulin → salbutamol → removal. |
Pseudo-hyperkalaemia — always consider
Haemolysed sample: tight tourniquet, small needle, delayed transport.
Extreme thrombocytosis (platelets > 1000 × 10⁹/L): potassium released during clotting.
Extreme leukocytosis in CLL.
Delayed processing: send to lab within 1 hour and process promptly.
- Any K+ ≥ 6.5 mmol/L, or ≥ 6.0 with ECG changes — emergency.
- Weakness or palpitations + K+ ≥ 6.0 — immediate ECG.
- On ACE inhibitor / spironolactone with rising K+ — reassess drug + kidney function.
Hyperkalaemia workup
- 1Any ECG changes?IV calcium gluconate immediately.
- 2K+ ≥ 6.0?Insulin + glucose. Nebulised salbutamol. Stop RAAS blockers.
- 3Anuric AKI or refractory?Dialysis.
- 4Chronic, mild, on essential RAAS inhibitor?Patiromer or sodium zirconium cyclosilicate.
Related questions people ask
Frequently asked questions
- K+ ≥ 6.5 or ECG changes = emergency.
- Calcium first (myocardial protection).
- Insulin + glucose shifts potassium.
- Dialysis or new binders remove potassium.
- Always exclude pseudo-hyperkalaemia.
References
2 sources- UK Kidney AssociationHyperkalaemia Guideline (2023)
Emergency management.
ukkidney.org
- European Resuscitation CouncilCardiac Arrest in Special Circumstances
Emergency guidance.
erc.edu
Evidence Snapshot
This snapshot shows verified evidence records matched to this article. It is not a diagnosis or personal medical advice.
Serum magnesium reflects only a small fraction of total body magnesium, most of which sits inside cells and bone, so a normal serum magnesium value does not by itself exclude tissue-level magnesium depletion.
Limitation. Tests that better reflect intracellular magnesium exist but are not part of routine panels and may not change routine practice.
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