Coagulation Tests

Blood for the coagulation tests is mixed with trisodium citrate which removes calcium by chelation. The blood is then centrifuged, and the plasma, which is now calcium free, is used for the tests. The principle of measuring the clotting times is dependent on the addition of calcium chloride which initiates clot formation. The concentration of calcium chloride used is 0.025 mol/l. The plasma clotting times are compared with normal or control sample times.