21st May 2025

Classification of Hyponatraemia

Acute vs Chronic 

It is important to define whether a hyponatraemia is acute i.e. a duration of less than 48 hours or chronic i.e. a duration greater than 48 hours. See below sections for further information on the management. 

Fluid status 

Hyponatraemia is classified according to 3 sub-groups:

1. Hypovolaemia – volume depletion i.e. dehydration
2. Euvolaemia – a normal volume status 
3. Hypervolaemia – volume overload  

Therefore when defining a hyponatraemia we should consider:

1. Is the hyponatraemia mild, moderate or severe?
2. Is this acute or chronic? i.e. less than or greater than 48 hours in duration
3. What is the patient’s fluid status? i.e. hypovolaemic/ euvolaemic/ hypervolaemic
4. Is the patient symptomatic?

Being able to answer these 4 questions will allow us to determine an appropriate management plan for each patient.