Which of the following would help to differentiate between SIADH and psychogenic polydipsia?
SIADH is characterized by a high urine osmolality, whereas the hallmark of psychogenic polydipsia is a low urine osmolality because the patient is drinking too much water and diluting extracellular sodium levels. The level of ADH is often suppressed. In addition, SIADH is associated with low BUN Psychogenic polydipsia is associated with low serum osmolality also, but potassium levels would be elevated. Ref:Else T., Hammer G.D. (2010). Chapter 19. Disorders of the Hypothalamus & Pituitary Gland. In S.J. McPhee, G.D. Hammer (Eds), Pathophysiology of Disease, 6e.
Blood urea nitrogen (BUN) 16 mg/dL
Serum osmolality 265 mOsm/L
Serum potassium 4 meq/L
Urine osmolality 500 mOsm/L