Blood coagulation is a complex process that requires the functioning of several substances, called coagulation factors, in series, the most important of which are manufactured in the liver. If the concentration or activity of one or more of these factors is abnormal, coagulation could be too slow (risk of internal or external bleeding) or too intense with the possibility of clot formation (infarction, phlebitis, embolism, stroke, etc.). Each coagulation factor can be evaluated in isolation. Bleeding time can be used to measure the first steps of the coagulation cascade in a single step. In this test, the time required to stop the flow of blood from a small cut on the forearm is measured with a stopwatch and expressed in minutes.
Too long a bleeding time means that one or more coagulation factors are present in insufficient quantities or do not function properly. Extended bleeding times may result from genetic causes (von Willebrand’s disease, Bernard-Soulier Syndrome, Glanzmann Thrombasthenia) or acquired causes (drugs such as aspirin and nonsteroidal anti-inflammatory drugs, certain antibiotics and anticoagulants such as heparin, etc.). Vitamin C deficiencies, alcohol intoxication, kidney or liver failure, leukemia and other bone marrow disorders may also be involved.