From the Research
Diagnosing SIADH requires a systematic approach focusing on laboratory findings and clinical presentation, with the most recent and highest quality study 1 indicating that the diagnosis is established when a patient has hyponatremia with hypoosmolality, inappropriately concentrated urine, elevated urine sodium, and normal renal, adrenal, and thyroid function in the absence of diuretic use. The diagnostic criteria for SIADH include:
- Hyponatremia (serum sodium <135 mEq/L) with hypoosmolality (<280 mOsm/kg)
- Inappropriately concentrated urine (urine osmolality >100 mOsm/kg)
- Elevated urine sodium (>20-30 mEq/L)
- Normal renal, adrenal, and thyroid function in the absence of diuretic use
- Clinical euvolemia, with no signs of volume depletion or overload Additional criteria include normal acid-base balance, normal potassium levels, and low blood urea nitrogen and uric acid levels. Before confirming SIADH, it's crucial to exclude other causes of hyponatremia, such as hypothyroidism, adrenal insufficiency, and medication effects, as noted in 2, 3, 4, 5. Common causes of SIADH include malignancies, CNS disorders, pulmonary diseases, and medications like SSRIs, carbamazepine, and certain chemotherapeutic agents, as mentioned in 2, 3, 1, 5. A thorough history, physical examination, and evaluation of medication use are essential components of the diagnostic workup to identify the underlying cause of SIADH, as emphasized in 1.