Blood clots help stop bleeding. Blood clotting (coagulation) disorders are dysfunctions in the body's ability to control the formation of blood clots. These dysfunctions may result in
Too much clotting, leading to the development of excessive blood clots (thrombosis)
Abnormal bleeding means that people bruise and bleed too easily (see also Bruising and Bleeding Bruising and Bleeding Bruising or bleeding after an injury is normal (see also How Blood Clots). However, some people have disorders that cause them to bruise or bleed too easily. Sometimes people bleed without any... read more 
and How Blood Clots How Blood Clots Hemostasis is the body's way of stopping injured blood vessels from bleeding. Hemostasis includes clotting of the blood. Too little clotting can cause excessive bleeding from minor injury Too... read more ). Abnormal bleeding can result from disorders of
Blood clotting (coagulation) system
Platelets Platelet Disorders (cell-like particles that help in the clotting system)
Clotting disorders occur when the body is unable to make sufficient amounts of the proteins that are needed to help the blood clot, stopping bleeding. These proteins are called clotting factors (coagulation factors). All clotting factors are made in the liver. The liver requires vitamin K to make some of the clotting factors.
Sometimes there is an abnormality of blood coagulation that increases the risk of clotting (called thrombophilia Excessive Clotting Excessive clotting (thrombophilia) occurs when the blood clots too easily or excessively. Inherited and acquired disorders can increase blood clotting. Clots in larger blood vessels cause legs... read more ).
Disorders of coagulation can be
Hereditary
The result of some other disorder
Disorders of coagulation also occasionally develop on their own (spontaneously).
The most common hereditary coagulation disorders are
The primary causes of coagulation disorders that develop as a result of another disorder are
Development of circulating anticoagulants Clotting Disorders Caused by Circulating Anticoagulants Sometimes a malfunction of the body's immune system causes it to make antibodies that attack the person's own tissues (autoantibodies) instead of attacking foreign or dangerous substances. Such... read more (antibodies that decrease the activity of a specific clotting factor)
Severe liver disease (including cirrhosis Cirrhosis of the Liver Cirrhosis is the widespread distortion of the liver's internal structure that occurs when a large amount of normal liver tissue is permanently replaced with nonfunctioning scar tissue. The scar... read more
, hepatitis Overview of Hepatitis Hepatitis is inflammation of the liver. (See also Overview of Acute Viral Hepatitis and Overview of Chronic Hepatitis.) Hepatitis is common throughout the world. Hepatitis can be Acute (short-lived) read more , acute liver failure Liver Failure Liver failure is severe deterioration in liver function. Liver failure is caused by a disorder or substance that damages the liver. Most people have jaundice (yellow skin and eyes), feel tired... read more , or acute fatty liver of pregnancy Fatty liver of pregnancy Some liver disorders occur only during pregnancy. Others (such as gallstones, cirrhosis, or hepatitis) may have been present before the pregnancy, or they may occur coincidentally with the pregnancy... read more )
Tests of Blood Clotting
One commonly tested measure that affects the body's ability to stop bleeding is the count of the number of platelets Platelets The main components of blood include Plasma Red blood cells White blood cells Platelets read more 
. Less often, doctors test how well the platelets function.
Other tests can measure the overall, coordinated function of the many proteins needed for normal blood clotting (clotting factors). The most common of these tests are the prothrombin time (PT) and the partial thromboplastin time (PTT).
The levels of individual clotting factors can also be determined.
