Criteria

Severity

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

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

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

  • Severe: serum sodium <125 mEq/L

Time of onset

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

Acute hyponatremia:

  • Hyponatremia that is documented to have occurred over <48 hours. Cerebral edema occurs more frequently when hyponatremia develops over <48 hours.[2]

Chronic hyponatremia:

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

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

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