Deep vein thrombosis is a common condition that affects approximately 1 in 1,000 people per year. The consequences of misdiagnosis are important and can affect both quality and length of life. Only a small percentage of patients evaluated for DVT in fact have a DVT. Thus, the risks associated with anticoagulation treatment – primarily major and minor hemorrhage – are significant, making a reliable, consistent approach to diagnosis essential. The American College of Chest Physicians’ recently issued guidelines for diagnosis and management of DVT in which they emphasized that the diagnostic process be based on clinical assessment of pretest probability of DVT to determine which test should be ordered.
The first step in assessing a patent for DVT is to risk-stratify patients for the likelihood of DVT using signs, symptoms, and risk factors. This assessment can be done using validated, structured tools such as the Wells score, which characterizes patients having a low, moderate, or high probability of DVT. Low, moderate, and high likelihood of disease on the Wells score reflects a prevalence of DVT of 5%, 17%, and 53% respectively. Further testing with D-dimer assays or imaging studies or a combination of these studies is based on this risk stratification.
Dr. Neil Skolnik and Dr. William Vaughan
Patients with a low pretest probability for DVT
Recommended testing for patients stratified with a low pretest probability of first lower extremity DVT include initial testing with D-dimer or compression ultrasound (CUS) of the proximal veins. Initial testing with a moderately or highly sensitive D-dimer rather than proximal CUS is preferred.
In cases where either the D-dimer or CUS is negative, no further testing is needed. The advantage of initial testing with a D-dimer assay is that the vast majority of patients assessed for DVT will need no further testing performed after a simple initial blood test, since most low-risk patients will have negative D-dimer assays. A CUS of the proximal veins (vs. whole-leg US) should be completed if the initial D-dimer is positive, because a D-dimer test is a sensitive but not specific test for venous thromboembolic disease. If initial testing with CUS is positive, treatment for DVT should be started.
Patients with a moderate pretest probability for DVT
Recommended testing for patients stratified with a moderate pretest probability of first lower extremity DVT include initial testing with a highly sensitive D-dimer, proximal CUS, or whole-leg US. Initial testing with a highly sensitive D-dimer vs. ultrasound is preferred.
No further testing is needed if the initial highly sensitive D-dimer is negative. If the initial highly sensitive D-dimer is positive, either a proximal CUS or whole-leg US should be completed. In the case of a negative initial CUS, repeat proximal CUS in 1 week or testing with highly sensitive D-dimer assay is required. If the follow-up proximal CUS is negative or the initial proximal CUS and subsequent D-dimer is negative, no further testing is needed.
No further testing is needed if an initial whole-leg US is negative. Treatment for DVT should be initiated if initial proximal CUS is positive. If an isolated distal DVT is found on whole-leg US, serial testing should be completed to rule out proximal extension.
Patients with a high pretest probability for DVT
It is important to understand that D-dimer testing should not be used exclusively to rule out DVT in patients with a high pretest probability. Recommended testing for patients stratified with a high pretest probability of first lower extremity DVT include initial testing with proximal CUS or whole-leg US. If either ultrasound is positive in the initial study, treatment for DVT should be started.
An initial negative proximal CUS should be followed up with a highly sensitive D-dimer or whole-leg US or by repeating the proximal CUS in 1 week. If a single proximal CUS is negative but D-dimer positive, a follow-up whole-leg US or repeat CUS is needed in 1 week. No further testing is needed if serial proximal CUS; a single proximal CUS, and highly sensitive D-dimer; or a whole-leg US are negative.
Patients without risk stratification
Recommended testing for patients not risk stratified with a first lower extremity DVT include initial testing with proximal CUS or whole-leg US. If the initial proximal ultrasound is negative, follow-up testing should be completed with a moderate- or high-sensitivity D-dimer, whole-leg US, or repeat proximal CUS in 1 week. In this case, follow-up testing with D-dimer is preferred. If a single proximal ultrasound is negative and the D-dimer is positive, then whole-leg US should be completed or a repeat proximal CUS in 1 week. No further testing is needed in patients with negative serial proximal CUS, a negative D-dimer following a negative initial proximal CUS, or negative whole-leg US. Treatment for DVT is recommended if proximal ultrasound is positive. Serial testing should be performed to rule out proximal extension if an isolated distal DVT is found on whole-leg US.