Next Step: CT Pulmonary Angiography (CTPA)
A moderate (intermediate) probability V/Q scan is non-diagnostic and requires further imaging with CT pulmonary angiography to confirm or exclude PE, regardless of whether the patient is already on anticoagulation. 1
Why CTPA is Required
A moderate probability V/Q scan falls into the "non-diagnostic" category, meaning it neither confirms nor excludes PE with sufficient certainty to guide treatment decisions. 1 The fact that the patient is already on Eliquis (apixaban) does not change this diagnostic imperative—you need definitive confirmation of PE presence before continuing, adjusting, or stopping anticoagulation. 1
The 2019 ESC Guidelines explicitly state that non-diagnostic V/Q scans necessitate further diagnostic testing. 1 The high frequency of non-diagnostic scans is a well-recognized limitation of V/Q scanning, and various strategies have been proposed to overcome this, with CTPA being the primary solution. 1
Integration with Clinical Probability
The interpretation of a moderate probability V/Q scan should be integrated with your clinical assessment: 1
If clinical probability is LOW: A moderate probability V/Q scan combined with negative proximal compression ultrasound (CUS) of the legs may be sufficient to exclude PE in some cases. 1 However, this approach requires careful consideration and many clinicians would still proceed to CTPA for definitive diagnosis. 1
If clinical probability is INTERMEDIATE or HIGH: CTPA is mandatory because the combination of moderate-to-high clinical suspicion plus a non-diagnostic V/Q scan leaves unacceptable diagnostic uncertainty. 1
Additional Diagnostic Considerations
Consider adding bilateral lower extremity compression ultrasound to look for deep vein thrombosis (DVT). 1 If proximal DVT is found, this confirms venous thromboembolism and supports the diagnosis of PE, though CTPA may still be warranted to assess clot burden and guide management. 1
Management During Workup
Continue therapeutic anticoagulation with Eliquis while pursuing definitive imaging, unless there are new contraindications to anticoagulation (active bleeding, recent major surgery, etc.). 2, 3 The ESC recommends continuing anticoagulation during diagnostic workup when clinical suspicion remains high. 2
Common Pitfall to Avoid
Do not assume that being on Eliquis means PE is already treated and no further workup is needed. The patient may have been started on Eliquis for another indication (atrial fibrillation, prior VTE), or may have developed PE despite anticoagulation (treatment failure, subtherapeutic dosing, or progression of existing clot). 3 You need definitive diagnosis to determine whether the current anticoagulation regimen is appropriate or needs modification. 3
Alternative: Pulmonary Angiography
If CTPA is contraindicated (severe contrast allergy, severe renal failure) or shows discrepant results with clinical assessment, pulmonary angiography should be considered as the historical gold standard. 1 However, this is rarely performed in modern practice given CTPA's excellent diagnostic accuracy. 1