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 blood clot is a mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding. Blood clotting is an important process that prevents you from losing too much blood when you are injured.

Normally, your body will dissolve the clot once your injury has healed. With a blood clotting disorder, clots can form when you don’t have an injury, or they don’t dissolve when they should. These disorders can be serious and even life-threatening.

Other names: fragment D-dimer, fibrin degradation fragment