In the nineteenth century, Rudolph Virchow proposed a theory concerning hemostasis. He believed that thrombosis was the result of a delicate interplay between three pro-coagulative factors: stasis, hypercoagulability, and vessel injury. To better illustrate this notion, he created a diagram shown below.
Since that time, the basic and clinical sciences have blossomed. We have a greater understanding of how the body achieves hemostasis by forming a clot when blood vessel injury occurs, stopping propogation of the clot at the right time, and then dissolving the clot when the vessel has healed. Our knowledge has revealed an interplay between a series of biochemical reactions called the coagulation cascade. Analogous to a play, the stage is the blood vessel wall or endothelium. The actors are platelets, phospholipid membranes, and coagulation factors (proteins that circulate in the blood). The protagonists are the coagulation factors while the antagonists are regulatory proteins that have the ability to inhibit coagulation. In a normal individual, all of these actors create a balance of clot formation and dissolution in order to achieve hemostasis while preventing either excessive thrombosis or bleeding.
Disruption of this balance, however, results in a spectrum of diseases, many of which are life-threatening and often fatal. On one extreme lies excessive thrombosis, resulting in blockage of blood vessels and eventual ischemia of tissues. On the other extreme is excessive bleeding, leading to conditions in which mucous membrane or joint space bleeding is common and dangerous. In between these extremes are patients who have mild disease and develop clotting or bleeding problems only after some inciting event such as surgery, trauma, or administration of certain drugs. Regardless of where they fit in this spectrum, these patients can indeed live a very healthy and normal life if their disease process is effectively diagnosed and managed. For many, treatment with medication or blood products will be lifelong, while for others it will be only during exacerbations, after trauma, or perioperatively.
This project was designed to acquaint the reader with an important aspect of hemostasis, namely the coagulation cascade. The cascade, its regulatory components, and its role in hemostasis will first be introduced. The focus will then shift to the disruption of hemostasis toward hypercoagulability, bleeding diatheses, and a combination of the two. This will be followed by a discussion of the common laboratory tests used in the diagnosis, monitoring, and treatment of this spectrum of diseases.
The overall aim of this project was for me to achieve a greater understanding of the coagulation cascade, its disorders, and essential laboratory tests while providing a teaching tool directed at all levels of medical education. Please fill out the evaluation page at the end of this project. Comments and corrections will be greatly appreciated and will be of tremendous help in maintaining this information.