D-dimer
What it measures, and what changes the number.
D-dimer is a protein fragment released when a blood clot is broken down by the body. The test measures these fibrin degradation products in plasma, giving an indication of recent clot formation and breakdown. Spanish language reports may list it as 'Dímero D' with a description of fibrin degradation products.
It is often ordered with clotting tests such as prothrombin time, INR and APTT, along with a platelet count, to look at the coagulation system as a whole.
The sample is drawn into a citrate tube, and underfilled or clotted tubes can affect the result. D-dimer assays differ considerably between manufacturers, and labs report results in different unit types (fibrinogen equivalent units or D-dimer units), so values from different labs are often not comparable. Age, pregnancy, surgery and inflammation also influence the level.
Often read alongside: Prothrombin time, INR, APTT, Platelets