Blood Clotting
How quickly and how well your blood clots.
13 tests explained
Common follow-up tests
- Activated Partial Thromboplastin Time (aPTT)A clotting-time test that shows how many seconds your blood takes to clot, and is also used to monitor heparin treatment.
- Antithrombin ActivityMeasures how well antithrombin, a natural brake on blood clotting, is working in your blood.
- D-Dimer (FEU)A blood test for fragments left when a clot breaks down, used to help rule out a blood clot and to follow clotting problems such as DIC.
- Factor VIII ActivityMeasures how well factor VIII, a clotting protein that is low in hemophilia A, is working in your blood.
- Fibrinogen ActivityMeasures how much working fibrinogen, the protein that forms the mesh of a blood clot, is in your blood.
- INR (International Normalized Ratio)A standard way to report how long your blood takes to clot, used mainly to monitor warfarin and to check clotting and liver function.
- Lupus AnticoagulantA clotting-time test for lupus anticoagulant, an antibody effect that slows clotting in the lab even though it is linked to clots in the body.
- Protein C ActivityMeasures how well protein C works. Protein C is a natural blood thinner made in the liver that helps keep your blood from clotting too easily.
- Protein S ActivityMeasures how well protein S works. Protein S is a natural blood thinner that helps protein C keep your blood from clotting too easily.
- Protein S, Free AntigenMeasures the active, unbound form of protein S, a natural blood thinner. It is the test many labs use first to look for low protein S.
- Prothrombin Time (PT)How many seconds your blood plasma takes to clot in the lab. It checks several clotting proteins and is used to follow warfarin.
- von Willebrand Factor Activity (Ristocetin Cofactor / GPIb Binding)Measures how well von Willebrand factor helps platelets stick to a wound. It is one of the main tests used to look into von Willebrand disease.
- von Willebrand Factor Antigen (VWF:Ag)Measures how much von Willebrand factor is in your blood. It is usually ordered with VWF activity and factor VIII to look into von Willebrand disease.