Haemostasis

Haemostasis is the body's normal physiological response for the prevention and stopping of bleeding/haemorrhage. It results in the blocking of any vascular breach. Generally speaking, it helps ensure blood fluidity and blood vessel integrity. Abnormalities in haemostasis can result in bleeding (haemorrhage) or blood clots (thrombosis).

Haemostasis consists of:

  • Primary Haemostasis with:
    • Local vascular contraction (to reduce blood flow to the injury site)
    • platelet plug formation
  • Clotting of the plasma (secondary haemostasis), involving interaction between numerous factors and inhibitors.
  • Fibrinolysis - process for removing the clot once blood vessel integrity has been restored.

When there is a breach in a blood vessel, the first priority (primary haemostasis) is to "plug" this breach. The main players in the blood are the platelets and Fibrinogen: these react together and block the breach by the formation of a platelet plug.

Figure 1: Formation of the clot. (Source: Introduction à l'étude de l'hémostase et de la thrombose - B. Boneu, J-P. Cazenave - 1997) Bleeding at the site of the vascular injury is stopped by the formation of an extravascular clot. An injury causes a transitory vasoconstriction of the small blood vessels reducing blood flow. Platelets stick to the sub-endothelial tissue at the site of injury and finally they aggregate together. Initiation of coagulation leads to the formation of fibrin, which helps stabilise this clot and stops bleeding.

Brêche = Breach
Epanchement sanguin = Bleed/haemorrhage
Aggrégation plaquettaire = platelet aggregation
Adhésion plaquettaire = platelet adhesion
Activation de la coagulation = activation of coagulation
Fibrine = fibrin

Following this first step, the formation of a clot (coagulation) stops any further bleeding (secondary haemostasis). This process consists of a series of chemical reactions involving various plasma components. To date 10 major coagulation factors are known to be involved in this process. These complex interactions lead to the transformation of a soluble protein, the fibrinogen, into an insoluble protein, the fibrin, which forms the frame of the clot Wound healing finally closes the bridge and fibrinolysis dissolves the clot.

Abnormalities in Coagulation

Coagulation problems are diagnosed by laboratory examination of the blood coagulation process, either by using a global test (clotting time), analytical test (looking specifically at the different components of coagulation) or by a 'blood count' (the amount of haemoglobin and the number of white cells, red cells and platelets per cubic millimetre of blood).

Some of these tests can also be used to measure the effect of any anticoagulant treatment that is given to treat or reduce the risk of thrombosis. Diagnostica Stago's activity is to develop and design the equipment and the different test methods that are used in the laboratory to measure and allow better understanding of coagulation/haemostasis.

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