Hyponatremia Guidelines

Updated: Aug 18, 2022
  • Author: Seyed Mehrdad Hamrahian, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Guidelines Summary

Two clinical practice guidelines on the diagnosis and treatment of hyponatremia, one from a United States expert panel and one a joint venture of three European societies, define hyponatremia as follows [3, 46] :

  • Mild: serum sodium concentration 130–135 mmol/L 
  • Moderate: serum sodium concentration 125–129 mmol/L
  • Severe: serum sodium concentration < 125 mmol/L
  • Acute: documented as lasting < 48 h
  • Chronic: documented as lasting ≥48 h, or duration cannot be classified

The guidelines recommend that in case of hypertonic and isotonic hyponatremia, address the underlying cause. The European guidelines state that hyponatremia with a measured osmolality < 275 mOsm/kg always reflects hypotonic hyponatremia.

To differentiate the cause of hypotonic hyponatremia, the guidelines recommend interpreting the osmolality of a spot urine sample as the next step followed by urine sodium check:

  • If urine osmolality is ≤100 mOsm/kg, consider this maximally dilute urine with relative excess water intake or low solute intake (such as in polydipsia or beer potomania)
  • If urine osmolality is >100 mOsm/kg, consider the presence of ADH (physiologic or non-physiologic)
  • Check the urine sodium concentration on a spot urine sample taken simultaneously with a blood sample to help differentiate further
  • If urine sodium concentration is < 20 mmol/L, it suggest a low effective arterial volume as a cause
  • If urine sodium concentration is >30 mmol/L, assess extracellular fluid status and use of diuretics to further differentiate likely causes of hyponatremia
  • Measuring vasopressin for confirming the diagnosis of SIADH is not suggested.


For comparison of the US and European guideline treatment recommendations, see the table in Treatment/Approach Considerations.

Treatment of patients with severe symptoms

For severe symptomatic hyponatremia prompt infusion of hypertonic 3% saline in the first-hour of management is recommended. It is recommended to monitor patients in an environment where close clinical monitoring can be provide with the serum sodium concentration checked in short intervals while repeating an infusion of hypertonic 3% saline

For patients whose symptoms improve after a 4-6  mmol/L increase in serum sodium concentration in the first hour, guideline statements include the following:

  • Avoid further hypertonic 3% saline.
  • Start a diagnosis-specific treatment if available, aiming at least to stabilize the sodium concentration.
  • Limit the increase in serum sodium concentration, as outlined in the table during the first 24 hours and during every 24 hours thereafter if hyponatremia is not true acute hyponatremia.

Treatment of patients with moderately severe symptoms

  • For hyponatremia with moderate symptoms consider hypertonic 3% saline
  • Start prompt diagnostic assessment and provide cause-specific treatment.
  • Limit the increase in serum sodium concentration to avoid potential harm and risk of ODS in the chronic hyponatremia
  • If possible, stop fluids, medications, and other factors that can contribute to or provoke hyponatremia.

Treatment of patients without severe or moderately severe symptoms

  • Make sure that the serum sodium concentration has been measured using the same technique used for the previous measurement and that no administrative errors in sample handling have occurred.
  • If possible, stop non-essential fluids, medications, and other factors that can contribute to or provoke hyponatremia.
  • Start prompt diagnostic assessment.
  • Provide cause-specific treatment.
  • Monitor clinical picture and serum sodium concentration closely.
  • Avoid an increase in serum sodium concentration above the limits outlined in the table in the setting of chronic hyponatremia.

Correcting overcorrection

If hyponatremia is corrected too rapidly, do the following:

  • Promptly initiate electrolyte free water, as outlined in the table, to re-lower the serum sodium concentration
  • Discontinue the ongoing active treatment. 
  • Consult an expert to discuss whether it is appropriate to add IV desmopressin