Syndrome of inappropriate antidiuretic hormone laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vindhya BellamKonda, M.B.B.S [2]

Laboratory findings which are helpful in diagnosing syndrome of inappropriate antidiuretic hormone (SIADH) include serum electrolytes (especially sodium), blood urea nitrogen (BUN), creatinine, glucose levels, and osmolality. Laboratory findings in patients with SIADH may show hyponatremia (sodium <135 mEq/L) and low serum osmolality (< 280 mOsm/kg). Patients with SIADH have elevated urinary sodium level (> 20 mMol/L) and urine osmolality (generally > 100 mOsm/L). Patients with SIADH also have low BUN, normal creatinine, hypouricemia, and hypoalbuminemia.

Laboratory findings consistent with the diagnosis of SIADH include:^{[1][2][3][3][4][5]}

• Hyponatremia (< 135 mEq/l)
• Hypoosmolality (< 280 mOsm/kg)
• Low BUN levels
• Hypoalbuminemia
• Hypouricemia
• Normal creatinine
• Normal thyroid hormones
• Normal cortisol
• Increased GFR
• Increased plasma ADH levels