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What is After administering 'desmopressin', urine osmolality should increase by how much in central diabetes insipidus? and explain in detail?
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 mOsm/kg 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 mOsm/kg; the level of circulating AVP will help differentiate the underlying cause, i.e., NDI versus central DI. Ref: Harrison 19e pg: 302