A patient presents to a clinic with complaints of headache fatigue. Lab data show serum sodium, 122 mEq/L; serum osmolality, 240 mOsm/L; urine osmolality, 455 mOsm/L. which condition best correlates with these data?
High-Yield Explanation
Hyponatremia, hypo-osmolality, and inappropriately concentrated urine are characteristic of SIADH. The syndrome results from excessive secretion of vasopressin. This could be due to ectopic tumor secretion of vasopressin, various central nervous system complications, or it could be drug induced. The increased vasopressin causes excessive water retention, resulting in dilutional hyponatremia and hypo-osmolality. Volume expansion inhibits the renin- angiotensin system. Plasma aldosterone therefore tends to be low, which partly explains the inappropriately concentrated urine.