What are the European clinical practice guidelines on the diagnosis and treatment of hyponatremia?

Updated: Jun 17, 2019
  • Author: Eric E Simon, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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A joint European clinical practice guideline on the diagnosis and treatment of hyponatremia has been published. The guideline defines hyponatremia as follows [2] :

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

The guideline recommends excluding hyperglycemic hyponatremia by measuring the serum glucose concentration and correcting the measured serum sodium concentration for the serum glucose concentration if the latter is increased, using the following formula:

Corrected serum Na+ = measured Na+ + 2.4 × ([glucose  – 100 mg/dL] /100 mg/dL)

If glucose is measured in mmol/L, 5.5 mmol/L is substituted for 100 mg/dL.

Related recommendations include the following:

  • Hyponatremia with a measured osmolality < 275  mOsm/kg always reflects hypotonic hyponatremia

  • Hyponatremia can be considered hypotonic in the absence of evidence for causes of non-hypotonic hyponatremia  (eg, glucose, hyperosmolar contrast media)

To differentiate the cause of hypotonic hyponatremia, the guideline recommends interpreting the osmolality of a spot urine sample as the first step, as follows:

  • If urine osmolality is ≤100 mOsm/kg, accept relative excess water intake as a cause of the hypotonic hyponatremia 
  • If urine osmolality is >100 mOsm/kg,  interpret the urine sodium concentration on a spot urine sample taken simultaneously with a blood sample 

Related guideline suggestions are as follows:

  • If urine sodium concentration is ≤30  mmol/L, accept 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 the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is not suggested.

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