Adjusting D-dimer cutoffs could safely eliminate many CT angiograms to rule out PE

By Salynn Boyles, Contributing Writer, MedPage Today

Tweaking a widely accepted strategy for assessing pulmonary embolism risk ruled out thrombosis and reduced chest imaging by a third among low-risk patients enrolled in a prospective study.

Assessment of clinical pretest probability (C-PTP, calculated by the Wells score) and blood D-dimer level are used to assess pulmonary embolism risk, with a low C-PTP and a D-dimer level of less than 500 ng/mL widely considered to rule out thrombosis.

But a prospective study by Clive Kearon, MB, PhD, of McMaster University in Hamilton, Ontario, and colleagues, confirmed earlier preliminary data showing that in low-risk patients, determined by C-PTP, raising the D-dimer threshold to 1,000 ng/mL still effectively rules out pulmonary embolism.

Among 1,285 patients with a low C-PTP and 40 patients with moderate C-PTP and a negative D-dimer test (less than 1,000 or less than 500 ng/mL, respectively) none had a venous thromboembolism during follow-up (95% CI 0.00-0.29%), they reported in the New England Journal of Medicine.

And this included 315 patients who had a low C-PTP and a D-dimer of 500 to 999 ng/mL (95% CI 0.00-1.20%).

"I think this should be practice changing," Kearon told MedPage Today. "But in order for practice to change you have to get clinicians on board. This will take time to translate into practice. But I believe many clinicians recognize that they are doing a lot of CTs and that the yield from this imaging is low. I think they will welcome a strategy to reduce the number of CTs they perform."

He explained that chest imaging with computed tomography (CT) pulmonary angiography is widely used to assess lung clot risk, but that only about 10% of patients who receive the imaging are found to have a pulmonary embolism.

"In North America about 10% of patients worked up for a clot on the lung actually have one," Kearon said. "The thinking was that if we could use these [screening] tests with more sophistication, we could exclude a higher proportion of patients from consideration of CT."

In the study, using the 500 ng/mL threshold to rule out pulmonary embolism for the low C-PTP patients would have resulted in 51.9% being sent for chest CT, but the team's diagnostic strategy of using a D-dimer level of less than 1,000 ng/mL resulted in chest imaging for just 34.3% of the group, a 33.9% relative reduction.

Kearon and colleagues' Pulmonary Embolism Graduated D-Dimer (PEGeD) study included 2,107 patients assessed for pulmonary embolism risk in the outpatient (emergency department or outpatient clinic) setting. Pulmonary embolism was considered to be ruled out in patients with a low C-PTP (using the Wells score) and a D-dimer of less than 1,000 ng/mL or with a moderate C-PTP and a D-dimer of less than 500 ng/mL.

Chest CT imaging was performed in patients who did not meet these thresholds, and patients without a diagnosis of pulmonary embolism did not receive anticoagulant therapy. Patients were followed for 3 months after initial assessment.

A total of 7.4% of evaluated patients had pulmonary embolisms on initial diagnostic testing.

Among the 1,863 patients who did not receive a diagnosis of pulmonary embolism at first assessment and did not receive anticoagulant therapy, one patient had a venous thromboembolism (0.05%, 95% CI 0.01-0.30).

Study limitations, the team said, included that all but one patient was recruited from outpatient settings, limiting the study's generalizability to hospitalized patients, and that there were too few patients with a moderate C-PTP and a D-dimer of less than 500 ng/mL to accurately identify the negative predictive value in the subgroup.

Funding for the study was provided by the Canadian Institutes of Health Research.

Kearon reported having no relevant relationships with industry related to this study.

Source: New England Journal of Medicine