Refer a patient with hyponatraemia to secondary care if they have acute onset (less than 48 hours) or severe hyponatraemia (serum sodium less than 125 mmol/L) and are symptomatic, or if they show signs of hypovolaemia NICE CKS.
Arrange an urgent 2-week wait referral for asymptomatic, moderate hyponatraemia (serum sodium 125–129 mmol/L) if malignant disease is suspected as an underlying cause of SIADH NICE CKS.
Refer if the cause of hyponatraemia is not clear, or if SIADH or other endocrine causes are suspected, as these require specialist input for diagnosis and treatment NICE CKS.
Discuss with an endocrinologist about the need for admission or referral if the patient has hyponatraemia with moderate symptoms (serum sodium 125–129 mmol/L) NICE CKS.
Consider urgent referral or admission if Addison's disease is suspected, or if reset osmostat syndrome or cerebral salt-wasting is suspected NICE CKS.