D-Dimer: The "Footprint" Your Blood Leaves After Clot Formation What is D-Dimer D-Dimer is a small protein fragment produced when blood clots dissolve. To understand it simply: when your body forms a blood clot (a process called coagulation) and later breaks it down (fibrinolysis), D-Dimer is the "footprint" left behind. Key fact: D-Dimer can only be produced when both thrombin (clot formation) an...