ELISA uses antigen-coated microtiter plates for the detection of ANAs. Each well of the microtiter plate is coated with either a single antigen to detect a specific antibody or multiple antigens to screen for ANAs in general. Serum is incubated in the wells of the plate and, after washing out the plates, any antibodies that bind to antigen will remain on the plate. A secondary anti-human antibody conjugated to an enzyme, such as horseradish peroxidase, is added to the plate. After an incubation period, an enzyme reaction will occur that produces a color change in the solution that is proportional to the amount of antibody bound to the antigen.
A positive result from the ELISA method will be a number of units that is above the laboratory's reference number (cutoff) for the lowest possible value that is considered positive.