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,
Activated clotting time of comparison due to inconsistencies between the source and formulation of the activator being used. It is usually ordered in situations where the partial thromboplastin time (PTT) test may take an excessive amount of time to process or is not clinically useful. Prolongation of the ACT may indicate a deficiency in coagulation factors, thrombocytopenia or platelet dysfunction. Clotting time measurements can be affected by other drugs that such as Warfarin, aprotinin and GPIIb/IIIa inhibitors and may also be affected by physical perturbations to the body such as hypothermia, hypervolemia or hypovolemia. Activated clotting time Activated clotting time (ACT), also known