ELISA antibody test. Technician carrying out an enzyme-linked immunosorbent assay (ELISA) antibody test. She is using a multichannel pipette to place samples into a multi-well sample tray. The ELISA test checks for antibodies to viral diseases such as AIDS (acquired immune deficiency syndrome) and hepatitis B and C. In the test, the patient's blood plasma is washed over a surface covered in the antigens of the virus being tested for. If the antibody is present then it will bind to these antigens. Next, peroxidase is added which binds to the antibodies. Then a chemical is added that changes colour when it comes in contact with peroxidase. Photographed in Iran.