A D-dimer test looks for D-dimer in blood. D-dimer is a protein fragment (small piece) that's made when a blood clot dissolves in your body. D-dimer isn't usually found in your blood unless your body is making or breaking up blood clots.

A D-dimer test is used to check if you may have a blood clot. The test helps to find out if you need more tests to check for blood clotting disorders. A D-dimer test may also be used to monitor how well treatments for a blood clotting disorder like disseminated intravascular coagulation (DIC) are working.

Source: MedlinePlus, U.S. National Library of Medicine