Diagnostic value of D dimer in pulmonary embolism and pneumonia

Diagnosis of pulmonary embolism (PE) and its clear-cut differentiation with other entities of occasional similar presentation remains difficult in routine clinical practice. High plasmatic levels of D dimer (DD), a specific fibrin derivate, have recently been reported in PE.

The purpose of this study was to prospectively evaluate the diagnostic value of plasmatic DD in a clinical setting.

We studied 52 patients with PE proven with pulmonary scintigraphic studies in relation to 19 patients posteriorly diagnosed of having community-acquired pneumonia and 30 healthy subjects. Evolution of DD levels whilst the patients were on intravenous anticoagulant therapy was evaluated by measuring DD concentration on admission and on day 7 in 10 patients.

Plasma DD levels were significantly higher in PE in relation to controls (p < 0.001). DD levels were also higher in patients diagnosed with community-acquired pneumonia in relation to controls (p < 0.05) but lower than those obtained in high probability PE (p < 0.05). Sensitivity and specificity of plasmatic DD in the emergency diagnosis of PE are of 92 and 71%, respectively. Plasma levels of DD were found to progressively decrease during the first week of heparin therapy, but they remained higher than in control subjects.

Plasma DD levels are increased in patients with suspected PE and the degree of elevation is related to the results obtained in scintiscans. Moreover, DD concentrations progressively decrease during the first week of anticoagulant therapy. The increased DD levels found in patients with pneumonia make this test useless in the differential diagnosis between these two clinical entities.