Autoimmune ELISA kits measure autoimmune antibodies in the serum. It is based on the principle of a solid phase enzyme-linked immunosorbent assay. The assay utilizes a specific antigen for immobilization on the microtiter wells and anti-mouse IgG antibody conjugated to horseradish peroxidase (HRP) for detection. The test sample is allowed to react simultaneously with the two components, resulting in autoimmune antibodies being sandwiched between the solid phase antigen and the enzyme-linked antibodies. After incubation, the wells are washed to remove unbound antibodies. Then an HRP substrate is added to develop a blue color. The color development is stopped with the addition of Stop Solution, changing the color to yellow. The concentration of autoimmune antibodies is directly proportional to the color intensity of the test sample. Absorbance is measured spectrophotometrically at 450 nm.