Coagulation studies are blood tests in which chemicals are added to a blood sample to calculate the amount of time it takes for a clot to form.
Different chemicals are used to measure different clotting factors in the blood. Coagulation studies may be done before surgery and are performed on patients who are taking blood thinners or to help diagnose bleeding disorders.
Prothrombin Time (PT)
PT is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot. The normal range is 11 to 13.5 seconds. However, “normal” varies from lab to lab.
International Normalized Ratio (INR)
If you are taking blood thinners due to heart attack, stroke, deep vein thrombosis or because you have an artificial heart valve, your clotting time will be longer, and another measure, the International Normalized Ratio (INR), will be used to calculate it. Because anticoagulant drugs must be carefully adjusted to maintain a balance between excessive clotting and excessive bleeding, periodic PT/INR tests are used to monitor clotting activity.
Partial Thromboplastin Time (PTT)
PTT measures one part of the clotting process—a group of coagulation factors produced in the liver. It may be used to diagnose lupus or to find a reason for recurrent miscarriages, especially those in the second or third trimester. The PTT is also used to monitor heparin anticoagulant therapy.
Date Last Modified: January 21, 2011
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