Management of Hyponatremia in Patients with Hypothyroidism

Diagnostic Workup

• Include hypothyroidism in the standard evaluation for syndrome of inappropriate antidiuretic hormone secretion (SIADH) together with adrenal insufficiency, diuretic use, heart failure, and cirrhosis, as recommended by the Chest guideline (2013) 1.

• Measure serum thyroid‑stimulating hormone (TSH) in every patient presenting with hyponatremia as part of the diagnostic algorithm, according to the Gastroenterology consensus (2025) 4.

Interaction with Adrenal Insufficiency

• Defer the diagnosis of subclinical hypothyroidism when adrenal insufficiency is present because untreated adrenal disease can falsely elevate TSH; TSH levels typically normalize after glucocorticoid therapy, per the Endocrine Practice guidance of the American College of Endocrinology (2012) 6.

Treatment of Severe Symptomatic Hyponatremia

• For patients with severe symptomatic hyponatremia (e.g., seizures or altered mental status), initiate standard hypertonic saline therapy irrespective of thyroid status, as outlined in the Chest protocol (2013) 1.

Consideration of Alternative Etiologies

• In hospitalized individuals, hyponatremia co‑occurring with hypothyroidism often reflects SIADH driven by other causes such as pulmonary infection, central nervous system disease, or medication effects rather than the thyroid disorder itself, according to the Pediatrics recommendation (2018) 7.