In a patient if administration of exogeneus vasopressin does not increase the osmolality of urine the likely cause is: (A) SIADH, (B) Psychogenic polydipsia, (C) Renal Hyposensitivity to ADH, (D) ADH Deficiency
Answer is C. 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).