Blot tests (Western Blot or immunoblot) indicate the presence or absence of antibodies against proteins constituent of a virus, parasite or bacteria or against antigens specific to some pathologies (e.g. auto-immune pathologies). The serum is incubated with specific strips, which contain antigenic proteins isolated along the nitrocellulose membrane. Should antibodies be present in the sample, colored bands appear at various spots on the strip, and allow the user to determine pathological profiles. These tests are usually used within the framework of confirmatory diagnosis.