This sandwich ELISA is designed with polyclonal antibodies coated onto the plate for capturing soluble forms of Angiotensin Converting Enzyme 2 (ACE2) in the tested sample. Following a washing step, captured ACE2 is tagged with aperoxidase-labelled polyclonal antibody, which binds onto its free epitopes in a dose-dependent manner. After washing away the excess of immunoconjugate, the substrate, 3,3′,5,5′ Tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) is introduced and a blue color develops, which turns yellow when the reaction is stopped with sulfuric acid. This color is measured at 450 nm, and is directly proportional to the amount of ACE2 present in the tested sample. Results are expressed in ng/ml, by reference to a plasma calibrator, supplemented with recombinant ACE2, and established against an internal reference preparation. ACE2, is a cell surface receptor, present on many cell types. It lowers blood pressure by converting angiotensin II (a vasoconstrictor) to angiotensin 1-7, a vasodilator. It is a major player of the Renin-Angiotensin-Aldosterone System (RAAS). ACE2 is also present in the soluble form in blood circulation, as the result of its extracellular domain cleavage by ADAM 17, releasing it from cell surface. The soluble form is essential for cleaving angiotensin II and lowering blood pressure. Increased concentrations of soluble ACE2 can be associated to various cardiovascular diseases.