Diagnostic workup of suspected DVT

Dr Wendy Lim is a professor in the Division of Hematology and Thromboembolism at McMaster University.

What should be the diagnostic workup in a patient with suspected deep vein thrombosis (DVT)?

Wendy Lim, MD, MSc: The workup in patients with suspected DVT ideally should incorporate an assessment of the clinical pretest probability followed by diagnostic testing. The reason we do that is that we would like to know the likelihood of a patient having venous thromboembolism (VTE) before we do testing because that guides our testing.

The vast majority of patients will have a low clinical pretest probability. In those patients we would suggest that D-dimer testing is a good test to do as a screening test, because if patients have a low clinical probability and then they have a negative D-dimer test result, that can essentially rule out the diagnosis.

However, some patients are likely to have VTE. Then the D-dimer test may be less helpful, because in many of those situations that test will be positive anyway. What we want to do if we really think they have VTE is we want to move to some objective diagnostic imaging. In the case of pulmonary embolism, it would be either a computed tomography (CT) scan, a pulmonary angiogram, or a ventilation/perfusion scan; for a lower extremity DVT, it would typically be a compression ultrasound with Doppler.