In a patient if administration of exogeneus vasopressin does not increase the osmolality of urine the likely cause is
Answer is C (Renal Hyposensitivity to ADH): Failure of urine osmolality to rise even after administration of exogenous ADH/vasopressin suggests a diagnosis of Nephrogenic Diabetes Insipidus due resistance to action of vasopressin on the Renal tubule (Renal Hyposensitivity to ADH).
SIADH
Psychogenic polydipsia
Renal Hyposensitivity to ADH
ADH Deficiency