What is dengue NS1 antigen lab test? Dengue infection can be diagnosed in laboratory via detection of virus, viral nucleic acid, antigens (substance from outside body’s environment) or antibodies (substance produced by body’s immune system to fight infection). In this test we detect NS1 (non-structural protein 1) antigen of dengue virus. This NS1 protein is secreted in blood during dengue infection. Why is dengue NS1 antigen lab test done? The test is done : As it helps in early detection ( < or = 7 days after fever onset) of dengue. This test not recommended after 7 days. It aids in confirmation of dengue infection in patients who have a travel history and clinical symptoms. When patients show flu-like symptoms and high grade fever characterized for dengue. As NS1 antigen is detectable during acute phase of dengue infection in blood.