Blood blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile"). The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A,
Dilute Russell's viper venom time specificity than the aPTT test for the detection of lupus anticoagulant, because it is not influenced by deficiencies or inhibitors of clotting factors VIII, IX or XI as the venom only activates factors V and X. Variations in the test can affect the results. The dRVVT is one component of a workup of a suspected antiphospholipid antibody, the other component being the serological testing for anticardiolipin antibodies and anti-β2 glycoprotein-I antibodies using ELISA technology. The Sapporo criteria require at least one of the above laboratory tests to be positive and the patient to have at least one clinical manifestation of