<prompt> After administering desmopressin, urine osmolality should increase by how much in central diabetes insipidus?At least 10At least 25At least 35At least 50  <response>: CDI NDI can be distinguished by administering AVP analogue desmopressin 10 mg intranasally after careful water restriction. Urine osmolality should increase by at least 50 in CDI will not change in NDI. Patients with NDI will fail to respond to DDAVP, with a urine osmolality that increases by 50 or 150 mOsmkg from baseline, in combination with a normal or high circulating AVP level; Patients with central DI will respond to DDAVP, with a reduced circulating AVP. Patients may exhibit a paial response to DDAVP, with a 50 rise in urine osmolality that nonetheless fails to reach 800 mOsmkg; the level of circulating AVP will help differentiate the underlying cause, i.e., NDI versus central DI. Ref: Harrison 19e pg: 302 