This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
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? 
Select and explain. 
A. Neurogenic diabetes insipidus, B. Nephrogenic diabetes insipidus, C. Diabetes mellitus, D. SIADH
D: SIADH
Answer: D: SIADH 
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.