Criteria

Severity

While there is no consensus on exact serum sodium values, hyponatraemia can be classified according to severity:[2][3]​​

  • Mild: serum sodium = 130-135 mmol/L

  • Moderate: serum sodium = 125-129 mmol/L

  • Severe: serum sodium <125 mmol/L

Time of onset

Hyponatraemia can be classified according to its time and speed of onset. In moderate and severe hyponatraemia the time of onset is crucial in determining the rate of correction.[3]

Acute hyponatraemia:

  • Hyponatraemia that is documented to have occurred over <48 hours. Cerebral oedema occurs more frequently when hyponatraemia develops over <48 hours.[2]

Chronic hyponatraemia:

  • Hyponatraemia that is documented to have occurred over ≥48 hours.

If hyponatraemia cannot be classified by time of onset, treatment should be based on symptoms.

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