DIAGNOSIS OF VTE
Surgeon General's Workshop on Deep Vein Thrombosis
Structured clinical assessment
- establish pretest probability
Symptoms and signs
Bedridden > 3 d or recent major surgery
Entire leg swollen
Calf swelling > 3 cm
Pitting edema in symptomatic leg
Low = 0; moderate 1-2; high = 3
Reference standard tests are expensive, invasive and require contrast
Photo of DVT: Venography
Photo of PE: Pulmonary Angiography
Degradation product of cross-linked fibrin
Assayed in plasma or whole blood
Sensitivity over 95%, but specificity only 65%
Test has high negative predictive value
Photo of SimpliRED D-dimer
- The SimpliRED assay is a whole blood assay that can be performed at the bedside using 10Âµl of blood obtained from either a venipuncture sample or on finger stick sample.
- The advantages of this assay over other methods of D-dimer detection include
- absence of a requirement for plasma preparation and, therefore,
- provision of a bedside result within 5 minutes
- a better specificity than the other classes of D-dimer assay (66-77%).
- However, the assay is a qualitative one that is manually read. Therefore, experience in obtaining results with this method is important. Because of difficulty in discriminating between weak positive and normal results, agreement among interpreters may vary.
Sensitivity and specificity over 95% for symptomatic proximal DVT
Sensitivity and specificity of 60 to 70% for isolated symptomatic calf DVT
Photo of Compression Ultrasonography (CUS)
Flowchart of suspected DVT Pretest Probability:
Patients with a low pretest probability of DVT should undergo D-dimer testing. If the D-dimer is negative, the risk of DVT is sufficiently low that further diagnostic testing is unnecessary. If the D-dimer is positive, CUS should be performed. A positive CUS establishes the diagnosis of DVT, whereas a negative test makes the diagnosis unlikely.
Those with a moderate or high pretest probability, where the prevalence of DVT is 33% and 85%, respectively, should proceed directly to CUS because a negative D-dimer cannot reliably exclude the diagnosis. A negative CUS in these patients does not exclude the possibility of calf DVT and a D-dimer test is helpful. A negative D-dimer makes calf DVT unlikely, whereas a positive test warrants repeat CUS in one week or sooner if symptoms progress.
Structured clinical assessment
CT angiography (or V/Q)
Photo of CT Pulmonary Angiography (CTPA)
Flowchart of suspected PE Pretest Probability:
Patients with a low pretest probability of PE should undergo D-dimer testing. A negative D-dimer excludes the diagnosis, whereas a positive test should prompt CTPA. Ventilation-perfusion lung scanning or MR angiography can be used in place of CTPA in patients with impaired renal function.
Patients with a moderate or high pretest probability should proceed directly to CTPA. A positive test establishes the diagnosis. Those with a negative or indeterminate test should undergo bilateral CUS and D-dimer testing. A positive CUS establishes a diagnosis of VTE. If CUS and D-dimer are both negative, the diagnosis is excluded. If CUS is negative, but the D-dimer test is positive, CUS should be repeated in one week.