How should I approach the management of a patient with SIADH who presents with mild hyponatremia?

For a patient with syndrome of inappropriate antidiuretic hormone secretion (SIADH) presenting with mild hyponatremia (serum sodium concentration of 130–135 mmol/L), the management approach in General Practice should involve several key steps.

• Initial Assessment and Monitoring: Ensure a repeat serum sodium measurement has been taken to rule out a rapidly decreasing serum sodium concentration, as this would necessitate immediate hospital admission NICE CKS. Asymptomatic, mild hyponatremia (130–135 mmol/L) may initially be managed in primary care NICE CKS.
• Fluid Restriction: Fluid restriction is a recommended management strategy for people with SIADH NICE CKS.
• Medication Review: Stop any non-essential medications that may be contributing to the hyponatremia, if appropriate, and recheck the serum sodium concentration after two weeks NICE CKS. If a contributing medication cannot be stopped, contact the appropriate specialist to discuss further management, monitoring, or referral NICE CKS.
• Treat Underlying Causes: If an acute illness is contributing to the hyponatremia, treat the underlying problem and recheck the serum sodium concentration after two weeks or sooner based on clinical judgment NICE CKS.
• Referral Considerations:
  • Discuss with an endocrinologist about the need for admission or referral if the person has asymptomatic, moderate hyponatremia (serum sodium concentration of 125–129 mmol/L) NICE CKS.
  • Refer to an endocrinologist if SIADH or another endocrine cause is suspected, with the urgency depending on clinical judgment NICE CKS. Specialist input is required to confirm the diagnosis and initiate treatment for hyponatremia related to an endocrine disorder NICE CKS.
  • Arrange an urgent 2-week wait referral to the appropriate specialist if malignant disease is suspected as an underlying cause of SIADH NICE CKS.
  • Tolvaptan, a medication for hyponatremia secondary to SIADH, should only be initiated in hospital or under specialist supervision NICE CKS.