Coagulation tests are blood tests that measure the time it takes for an individual’s blood to clot under standardized conditions. When the body has been injured, blood clots form to stem bleeding. Without blood clots to stop the bleeding, a person would bleed to death.

By measuring how well and how long it takes a patient’s blood to clot, coagulation tests can help diagnose illness. Some conditions can prevent blood from clotting properly, whereas others may cause the blood to clot too easily or cause clots to remain in the body too long.

In addition, coagulation tests can be used to monitor patients taking anticoagulants (medications that decrease the ability of the blood to clot). Anticoagulant medications are often prescribed to patients after they have suffered a heart attack or stroke. Those with arrhythmia (irregular heart beats) may also take anticoagulants to prevent a first or recurrent stroke. Coagulation tests may also be ordered to evaluate a patient’s risk of excessive bleeding before surgery.

There are many types of coagulation tests. Some are general and tell only whether or not a person’s blood is clotting normally. Other tests can identify which element within the blood is causing abnormal clotting. There are also tests to measure how well the body destroys blood clots that are no longer needed.