Hypokalaemia occurs more commonly and in a broad range of patients. However, hyperkalaemia is more serious and largely occurs in patients with some underlying renal or acid base abnormality [2].


Mild 3.0-3.5 mmol/L
Moderate 2.5-3.0 mmol/L
Severe <2.5 mmol/L

Hypokalaemia is defined as K(S) < 3.5 mmol/L. Symptoms are more likely with lower values.


Mild 5.5-5.9mmol/L
Moderate 6.0-6.5 mmol/L
Severe > 6.5 mmol/L

Hyperkalaemia is the most common electrolyte disorder associated with life threatening arrhythmias and cardiac arrest. It is defined as 5.5mmol/L [3].

Mild hyperkalaemia is common and often well tolerated in patients with chronic renal failure. K(S) > 10 mmol/L is usually fatal.

Learning bite

K(s) must always be checked in disturbances of cardiac rhythm.