# Acute hyperkalemia: potassium and the ECG

Andrew Bland, MD, FACP, FAAP · October 21, 2026

Recognize electrical toxicity; the ECG does not measure potassium.

## Read the level and the tracing together

The UK Kidney Association classifies potassium 5.5–5.9 mmol/L as mild, 6.0–6.4 as moderate and ≥6.5 as severe hyperkalemia. The tracing can show peaked T waves, PR prolongation, P-wave flattening or disappearance, QRS widening and eventually QRS–T fusion. These are illustrative patterns, not potassium-specific thresholds or a dependable sequence.

## Treat electrical toxicity promptly

A normal ECG does not exclude severe hyperkalemia. Interpret the potassium trend, symptoms, kidney function and ECG together. With convincing ECG toxicity, protect the myocardium with IV calcium while arranging potassium redistribution and removal. Calcium does not lower potassium. The clean repeat specimen and definitive treatment proceed alongside emergency care.

## Sources

- [UK Kidney Association: hyperkalemia guideline, updated July 2026](https://www.ukkidney.org/health-professionals/guidelines/treatment-acute-hyperkalaemia-adults-0)
- [KDIGO conference summary: acute hyperkalemia](https://pubmed.ncbi.nlm.nih.gov/32852924/)

[Open the infographic](https://urinenephrology.org/visual-reference/day1-hyperkalemia-ecg)