AIIMS November 2011 – MCQ 60

All are true regarding SIADH except?
A. Serum Na can be as low as 125 mEq/L
B. Urine sodium is normal or slightly low
C. Vaptans are new FDA approved drugs for its treatment
D. Water loading test is used for diagnosis

Correct answer : B. Urine sodium is normal or slightly low

In SIADH, serum Na is decreased, urine sodium is increased. Vaptans act by inhibiting the action of vasopressin on its receptors (V1A, V1B and V2).

Water loading test:
If SIADH is suspected in a patient with mild hyponatremeia, a water loading test can be performed to confirm the diagnosis.
Ref: Tietz’s applied laboratory medicine, Volume 564 By Mitchell G. Scott, Norbert W. Tietz, Ann M. Gronowski, Charles S. Eby (via google books)