Refer a patient with hyponatraemia to secondary care if they have acute onset (less than 48 hours) or severe (serum sodium less than 125 mmol/L) hyponatraemia, especially if they are symptomatic or show signs of hypovolaemia NICE CKS.
Arrange an urgent 2-week wait referral if the hyponatraemia is asymptomatic but moderate (serum sodium 125–129 mmol/L) and 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 or signs of hypovolaemia NICE CKS.