The principle of the assay is based on the general ELISA setup. The sample is coated onto a 96-well plate and incubated with the complex protein C1q. Next, the detection antibody (polyclonal anti C1q tagged with horseradish peroxidase (HRP)) is added to the plate. The detection antibody targets the C1q that is complexed to the coated sample and binds to the anti C1q antibody. After removing superfluous detection antibody, the chromogenic substrate 3,3,5,5-Tetramethylbenzidine (TMB) is converted by the HRP, resulting in a change in color that is directly proportional to the concentration of the sample. In the final step, this reaction is stopped by acidification and the optical density (OD) of each well is measured using the ELISA microplate reader SpectraMax.