The dengue NS1 antigen is a non-structural protein of the dengue virus that is secreted into the blood during dengue infection. It is detectable during the acute phase of the infection and can be used as a marker for the early diagnosis of dengue virus infections. NS1 tests have been developed for use in serum, and a positive NS1 test result confirms dengue virus infection without providing serotype information. However, a negative NS1 test result does not rule out infection, and people with negative NS1 results should be tested for the presence of dengue IgM antibodies to determine possible recent dengue exposure