What are the indications for referring a patient with SIADH to secondary care for further evaluation?

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Posted: 17 August 2025Updated: 17 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed
Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

For patients with syndrome of inappropriate antidiuretic hormone secretion (SIADH) or suspected SIADH, referral to secondary care is indicated in several situations:

  • Immediate Hospital Admission:
    • If the patient has acute onset hyponatraemia (duration less than 48 hours) or severe hyponatraemia (serum sodium concentration less than 125 mmol/L) .
    • If the patient is symptomatic .
    • If there are signs of hypovolaemia .
    • If a rapidly decreasing serum sodium concentration is observed .
  • Urgent 2-Week Wait Referral:
    • If malignant disease is suspected as an underlying cause of SIADH .
  • Referral to an Endocrinologist (urgency based on clinical judgement):
    • If SIADH or another endocrine cause of hyponatraemia is suspected .
    • If the cause of hyponatraemia is not clear, particularly if it is persistent and no cause can be identified in primary care .
    • If the patient has asymptomatic, moderate hyponatraemia (serum sodium concentration of 125–129 mmol/L) .
    • If the serum sodium concentration remains low after stopping a medication that may have been contributing to the hyponatraemia .
  • Specialist Supervision for Treatment:
    • Treatment with Tolvaptan for hyponatraemia secondary to SIADH should be initiated in hospital or under specialist supervision .

Related Knowledge Topics

Educational content only. Always verify information and use clinical judgement.