Post #32: Venous Thromboembolism – diagnosis and follow up imaging

Venous Thromboembolism (VTE) may present as either

• deep vein thrombosis (DVT) or

• pulmonary embolism (PE).

VTEs are potentially fatal diseases (30% of patients with VTE die within the first year after diagnosis). Because the signs and symptoms mimic other diseases (with much different treatments, such as cellulitis and superficial phlebitis, congestive heart failure and myocardial infarction) prompt and accurate diagnosis is critical for appropriate treatment and to avoid thrombus extension or embolization. Imaging is required to confirm the presence of VTE, but not every case of suspected disease requires imaging to rule it out. The use of diagnostic algorithms to assess pretest probability, and a simple rapid blood test, can help determine which patients need advanced imaging and which ones do not.

Although venous thromboembolism (VTE) may be a life-threatening condition that usually responds to anticoagulant treatment, less than 20% of patients initially suspected of having the diagnoses are confirmed using imaging. Modern imaging techniques often detect small potentially insignificant emboli, so it is not necessary to perform imaging in every suspected case. The American College of Chest Physicians and other organizations have established guidelines for the diagnosis of VTE that are used by radiology benefits management companies (RBM).

Based on clinical, laboratory and historical findings, it is possible to determine which patients with suspected VTE should advance to additional imaging studies, and which have such a low pre-test probability that imaging is not needed.

According to one RBM guideline, patients who exhibit at least one of the Pulmonary symptoms:

• new and otherwise unexplained dyspnea

• pleuritic chest pain or

• tachypnea

And one of the following sign, symptom, lab test or history

1. Abnormal d-dimer test

2. Wells Criteria score > 4 points

3. One Risk Factor (7 factors below) or

4. One PE related symptom (7 symptoms below)

may obtain authorization for an advanced imaging study for VTE.

Details of the above criteria

1. D-dimer test: a blood test that can be performed rapidly and has high sensitivity but low specificity so it may be used to rule out PE but cannot rule PE in. A negative D-dimer plus low or moderate pre-test probably by Wells Criteria has a negative predictive value of 100%. False positive D-dimer can occur with recent surgery, injury, malignancy, sepsis, diabetes, pregnancy or other condition elevating fibrin products. In patients with low to moderate clinical likelihood of PE (Wells Criteria score less than 4), a negative D-dimer means advanced imaging is not needed. In patients with moderate to high pre-test probability of PE and an elevated D-dimer, imaging with CTA or CT can be approved.

2. Wells Criteria for Probability of PE

The most often used clinical decision rule is the Wells criteria, which is made up of 7 clinical features with each feature assigned 1 to 3 points. These points are added together to determine the pre-test probability for Pulmonary Embolism. See below for the Wells Criteria:

Total Points Probability  <2 Low  2-6 Moderate  >6 High

Total Points Probability

<2 Low

2-6 Moderate

>6 High

Only ONE of the following 14 factors is required to obtain approval for CT chest PE protocol or CTA chest.

Risk factors for PE jpeg.jpg

Summary: If PE is suspected by respiratory symptoms, search for one abnormal feature in the 4 lists and categories. If one abnormality is found, advanced imaging may be requested and should be approved. If pretest probability (by Wells Criteria) shows a low likelihood of having PE, perform a D-dimer and if negative, PE is unlikely and imaging is not necessary.

Frequently Asked Questions

1. What is the recommended imaging study for suspected PE?

Chest CTA (71275) OR CT chest with contrast with PE protocol (71260).

Both of these imaging studies require IV contrast.

2. Are there other clinical decision rules for determining pre-test probability of PE?

yes, there are the revised Geneva score and the 8 criteria PERC (pulmonary embolism rule-out criteria). Variation criteria of D-dimer have been described as the age-adjusted D-Dimer for patients older than 50. However, none of these rules are used by radiology benefits management companies.

3. Rather than performing a high-radiation CT chest OR CTA chest, are there other alternative test for pregnant women or patients who have had large doses of radiation in the past?

Yes, there are two alternatives:

• One surrogate test for PE is a Venous Doppler. If Doppler is positive, one can safely proceed with anticoagulation, although this test does not prove a PE has occurred or identify its size, even with clinical chest symptoms of PE.

• Ventillation/Perfusion Scan is not a substitute for CT or CTA but can be used in pregnant women with positive D-dimer and negative Venous Doppler. It can also be used in patients if CT/CTA is contraindicated or equivocal.

3. Once a patient with documented PE is treated for a prescribed period of time (3-6 months) and is stable or asymptomatic, may an imaging study be performed to help determine if anticoagulation should be stopped?

No, clinical evaluation and risk factors should be used to make that decision without additional imaging. For example, if a clot is provoked by surgery, the risk of recurrence is low. A clot provoked by pregnancy, estrogens, and immobilization has a moderate risk of recurrence. Clots provoked by cancer or unprovoked have high risk of recurrence and prolonged anticoagulation should be weighed against the risk of bleeding. But in no instances to guidelines recommend repeating imaging studies without recurrence of symptoms.

A clot in the pulmonary artery, even with adequate anticoagulation, may persist in the artery 6 months after treatment in 2/3 of the cases of PE. 50% of cases of PE will demonstrate a PA clot after 1 year.

4. If D-dimer is positive at the time of diagnosis of PE and persists during or after treatment, can a post treatment imaging study be approved to assess risk and prolonged anticoagulation? Although persistence or elevation of D-dimer is associated with increased risk of recurrent PE, there is no evidence that repeating a CT or CTA will affect outcomes or predict another VTE. Clinical evaluation and risk factors should be used to make that decision without additional imaging.