What is the significance of a markedly elevated D-dimer level in the context of suspected pulmonary embolism?

A markedly elevated D-dimer level in the context of suspected pulmonary embolism (PE) indicates that there is likely ongoing or recent clot formation and breakdown in the body. D-dimer is a fibrin degradation product, a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. Fibrinolysis is the process by which the body breaks down blood clots. When a thrombus (blood clot) forms, fibrin is produced to stabilize the clot. As the clot breaks down, D-dimer is released into the circulation. An elevated D-dimer level suggests that there has been activation of the coagulation cascade and subsequent fibrinolysis. In the context of suspected PE, a markedly elevated D-dimer level increases the probability that a blood clot is present in the pulmonary arteries. However, it is important to note that D-dimer is not specific for PE. Elevated D-dimer levels can also be seen in other conditions, such as deep vein thrombosis (DVT), recent surgery, trauma, infection, cancer, pregnancy, and advanced age. Therefore, a D-dimer test is primarily used to rule *outPE in patients with a low or intermediate clinical probability of PE. A negative D-dimer result in these patients makes PE less likely, and further testing may not be necessary. However, a positive D-dimer result, especially a markedly elevated one, warrants further investigation to confirm or exclude the diagnosis of PE, typically with imaging studies such as CT pulmonary angiography (CTPA) or ventilation-perfusion (V/Q) scanning.