Prostaglandin E2 (PGE2), Leukotriene B4 (LTB4), Cyclic AMP and Cyclic GMP Competitive ELISA are based on the competition between eicosanoid in the standard or sample and alkaline phosphatase-conjugated eicosanoid, for a binding to a limited amount of eicosanoid-specific monoclonal antibody precoated onto a 96-well plate. As the concentration of eicosanoid in the sample increases, the amount of alkaline phosphatase-conjugated eicosanoid captured by the coating antibody decreases. Thus, there is an inverse relationship between optical density (OD) and the amount of eicosanoid in the sample.