The Dengue NS1 Antigen test is a blood test used to detect the non-structural protein 1 (NS1) of the Dengue Virus. 

• NS1 is a viral protein secreted by dengue virus-infected cells.
• It is present in the blood during the early phase of infection, usually from day 1 to day 7 after fever onset.
• Detection of NS1 allows for early diagnosis of dengue infection, even before antibodies (IgM/IgG) appear.