A 25-year-old woman has a 3-day history of vomiting and diarrhea. She has postural hypotension and poor tissue turgor. Her serum sodium concentration is 130 mEq/L. Which of the following findings is most likely?
(A) Decreased serum aldosterone concentration
(B) Increased serum atrial natriuretic peptide concentration
(C) Increased effective circulating volume
(D) Increased serum ADH (vasopressin) concentration
(E) Urine osmolality less than serum osmolality
Correct answer : (D) Increased serum ADH (vasopressin) concentration
Explanation: ADH secretion is increased during fluid depletion. Excluding the other options: A) Aldosterone’s function is to conserve water by increasing reabsorption. Hence the concentration will be increased. B) ANP is released in response to high BP to reduce water and sodium circulatory load. Hence it is not increased in this case. C) Since there is water loss with hypotension, circulating fluid volume will be low. E) Because body is conserving water urine osmolality will always be more than serum osmolality.