How are D-dimer results used to diagnose pulmonary embolism (PE)?

Updated: Jun 06, 2019
  • Author: Daniel R Ouellette, MD, FCCP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Answer

Combining D-dimer results with measurement of the exhaled end-tidal ratio of carbon dioxide to oxygen (etCO2/O2) can be useful for diagnosis of pulmonary embolism. Kline et al found that, in moderate-risk patients with a positive D-dimer (>499 ng/mL), an etCO2/O2< 0.28 significantly increased the probability of finding segmental or larger pulmonary embolism on computed tomography multidetector-row pulmonary angiography, while an etCO2/O2) >0.45 predicted the absence of segmental or larger pulmonary embolism. [51]

Because of the poor specificity, positive D-dimer measurements are not helpful in confirming the diagnosis of venous thromboembolic disease. However, a positive D-dimer measurement may lead to consideration of venous thromboembolic disease in the differential diagnosis in selected patients. In addition, the use of D-dimers in children is not well studied. A small pediatric series reported that D-dimer measurements are negative in 40% of patients. [29] A retrospective series reported an elevated D-dimer in 86% of patients at presentation. [17]


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