Classification of hyponatraemia

Hyponatraemia can be classified according to the serum sodium concentration (1):

• Mild — serum sodium concentration 130–135 mmol/L.
• Moderate — serum sodium concentration 125–129 mmol/L.
• Severe — serum sodium concentration less than 125 mmol/L

Classification according to volume status:

• hypovolaemic hyponatraemia
• euvolaemic hyponatraemia
• hypervolaemic hyponatraemia

Hyponatraemia is also classified according to the rate of onset (although calculating the duration of hyponatraemia is often difficult):

• acute hyponatraemia - symptoms develop in less than 48 hours
• chronic hyponatraemia - symptoms present for more than 48 hours

Reference:

1. Spasovski G, Vanholder R, Allolio B, et al; Hyponatraemia Guideline Development Group. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014 Feb 25;170(3):G1-47.