Key Point

D-dimer tests should be considered in conjunction with clinical probability of pulmonary embolism (PE) to determine patient risk.

D-dimer concentration alone may not be an effective marker to assess the probability of pulmonary embolism (PE) in patients suspected of having the disorder, reported Nadine S. Gibson, PhD, of the Department of Vascular Medicine at the Leiden University Medical Center in the Netherlands, and colleagues. D-dimer test results should not be used to exclude PE in patients with a likely clinical probability of PE; in these cases, further imaging tests should be conducted. “Although this strategy is recommended in several guidelines, in daily clinical practice physicians are often influenced by a normal D-dimer,” the authors suggested, citing previous studies. Patient examination and clinical probability for PE should be determined before D-dimer tests, they recommended. “[This] may prevent physicians from being influenced by a normal D-dimer test result when they evaluate the clinical probability,” the investigators emphasized in the October Chest.

The researchers identified for inclusion in the analysis 1,722 of 3,306 patients (mean age, 54) suspected of having PE, using data from a prospective management study conducted in hospitals across the Netherlands. Patients were excluded on the basis of age (< 18), low-molecular-weight heparin treatment (> 24 hours), pregnancy, known hypersensitivity to iodinated contrast fluid, life expectancy (< three months), geographic inability for follow-up, or lack of consent. The clinical probability of PE was assessed in all patients using the dichotomous clinical decision rule as set forth by Wells et al and Gibson et al, with a score of 4 or less representing an unlikely clinical probability to develop PE and a score greater than 4 a likely probability.

In patients with an unlikely probability of PE, D-dimer concentration was evaluated. Patients with normal D-dimer results (ie, ≤ 0.5 mg/L) deemed unlikely to develop PE were ruled out for PE diagnosis. A CT scan was performed in patients with likely PE or abnormal D-dimer results. At the three-month follow-up, which consisted of a medical visit or a phone interview, the researchers evaluated the rate of venous thromboembolism (VTE) among the patients.

A total of 563 (34%) of the 1,632 patients with available data had normal D-dimer concentrations. Of these, 13 patients were diagnosed with PE either at the time of the study or during follow-up, for a VTE rate of 2.3%. In 477 patients (28%), the probability of PE was unlikely and D-dimer results were normal; therefore, PE was ruled out.

VTE was confirmed during the three months’ follow-up in five of 477 patients (1.1%) with normal D-dimer concentration and unlikely clinical probability of PE. PE was confirmed in eight of 86 patients with normal D-dimer concentration and a likely probability of developing PE (9.3% VTE rate). The incidence of VTE between patients with a likely and unlikely clinical probability for PE was statistically significant, the investigators reported.

“This study convincingly illustrates that relying on D-dimer testing alone carries an unacceptable risk if the clinical probability of PE is not taken into account,” the authors concluded. “Clinicians need to realize that they should ignore a normal D-dimer concentration when the clinical probability is considered to be likely.”

—Frederique H. Theuvenin

Suggested Reading
Gibson NS, Sohne M, Gerdes VEA, et al. The importance of clinical probability assessment in interpreting a normal d-dimer in patients with suspected pulmonary embolism. Chest. 2008;134(4):789-793.
Gibson NS, Sohne M, Kruip MJ, et al. Further validation and simplification of the Wells clinical decision rule in pulmonary embolism. Thromb Haemost. 2008;99(1):229-234.
Wells PS, Anderson DR, Rodger M, et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thromb Haemost. 2000;83(3):416-420.

Return to table of contents