D-dimer

D-dimer is a fibrin degradation product. Its level in the blood correlates with the activity of coagulation and fibrinolysis. It’s highly sensitive for venous thromboembolism (including deep vein thrombosis and pulmonary embolism) and disseminated intravascular coagulation, in which case the level is increased.

However, D-dimer is not specific. It can be elevated due to other conditions, like pregnancy, cancer, infection, kidney disease, surgery, etc. Thus, D-dimer cannot be used for diagnosis of VTE or DIC but can be used to rule out VTE. It should not be measured in those with other conditions known to cause positive D-dimer.

If the pre-test probability for VTE is low and the D-dimer is normal, VTE is effectively ruled out (high negative predictive value). However, if the pre-test probability is moderate or high, there may still be VTE despite a negative D-dimer, so measuring the D-dimer is useless. The pre-test probability is estimated by calculating the Wells score.