Background: A pulmonary embolism can be considered ruled out if patients have a low C-PTP for PE and a D-dimer level of less than 500 ng/mL. However, this occurs in approximately 30% of outpatients only. By increasing the D-dimer threshold used to define a negative test to 1,000 ng/mL in patients with a low C-PTP, we might be able to rule out a larger segment of patients and avoid chest imaging.
Study design: Prospective study.
Setting: University-based clinical centers in Canada.
Synopsis: This study enrolled 2,017 patients presenting with symptoms of PE. The Wells’ criteria was used to categorize the patient’s C-PTP as low (0-4.0), moderate (4.5-6.0), or high (6.5 or more). Patients with a low or moderate C-PTP had a D dimer drawn. Those with a low C-PTP and D dimer of less than 1,000 ng/mL or moderate C-PTP and a D dimer of less than 500 ng/mL underwent no further testing. Outcomes were assessed at 90 days. Of the 1,325 patients with a low C-PTP or moderate C-PTP and a negative D-dimer test (less than 1,000 or 500 ng/mL, respectively), none had venous thromboembolism during follow-up (95% confidence interval, 0.00-0.29). This strategy resulted in the use of chest imaging in only 34.3% of patients versus 51.9% using the prior criteria of a D-dimer level of less than 500 ng/mL (difference, –17.6 percentage points; 95% CI, −19.2 to −15.9). One limitation of the study is that almost all patients enrolled were outpatients (only one inpatient).
Bottom line: A combination of a low C-PTP and a D-dimer level of less than 1,000 ng/mL identified a group of patients at low risk for pulmonary embolism during follow-up.
Citation: Kearon C et al. Diagnosis of pulmonary embolism with D-dimer adjusted to clinical probability..
Dr. Santa is assistant professor in the division of hospital medicine, Loyola University Medical Center, Maywood, Ill.