Human Surfactant Protein D / SP-D ELISA Kit (A312591) employs the sandwich enzyme immunoassay technique for the quantitative measurement of human Surfactant Protein D / SP-D in An antibody specific for Surfactant Protein D / SP-D has been pre-coated onto a 96-well microtiter plate. The standards and test samples are added into the wells and the Surfactant Protein D / SP-D present in each sample is bound to the wells by the immobilized antibody. Biotinylated Anti-Surfactant Protein D / SP-D Antibody, which also binds the Surfactant Protein D / SP-D present in each sample, and Streptavidin-HRP, which binds the Biotinylated Anti-Surfactant Protein D / SP-D Antibody, are added and the microtiter plate is incubated. Following incubation, unbound Biotinylated Anti-Surfactant Protein D / SP-D Antibody and unbound Streptavidin-HRP are removed by washing, and two substrate solutions are added to the wells. Color develops in proportion to the amount of Surfactant Protein D / SP-D captured in each well. The color development is stopped by addition of stop solution which changes the color from blue to yellow and the intensity of the color is then measured. The concentration of Surfactant Protein D / SP-D in the samples can then be calculated by reading the O.D. absorbance at 450nm in a microplate reader and referring to the standard curve.