CT Pulmonary Angiography (CTPA/CTA) for Elevated D-dimer with Dyspnea and Influenza A
Order CT pulmonary angiography (CTPA/CTA chest) as the definitive imaging study for this patient with elevated D-dimer and difficulty breathing, even in the setting of influenza A positivity. 1
Clinical Reasoning
Why CTPA is the Appropriate Choice
- CTPA is the primary imaging modality for evaluating suspected pulmonary embolism (PE) in patients with elevated D-dimer levels 1
- The 2022 ACR Appropriateness Criteria and 2014 ESC Guidelines establish CTPA as the second-line test after positive D-dimer in hemodynamically stable patients 1
- In patients with elevated D-dimer, CTPA should be performed rather than no imaging, as the D-dimer has already triggered the diagnostic algorithm 1
Critical Pitfall: Influenza Does NOT Exclude PE
- Influenza A positivity does not rule out concurrent pulmonary embolism 2
- D-dimer can be elevated in multiple conditions including infection, but this does NOT negate the need for PE evaluation when clinical suspicion exists 1, 2
- Recent evidence demonstrates that even very high D-dimer levels in symptomatic patients with respiratory infections may not indicate PE, but imaging is still required to definitively exclude it 2
- The combination of dyspnea and elevated D-dimer mandates PE exclusion regardless of alternative diagnoses like influenza 1
Why NOT Standard Chest CT
- Standard chest CT with IV contrast (non-angiographic timing) is not appropriate for PE evaluation 1
- The ACR guidelines explicitly state that CT chest with IV contrast is not supported for suspected PE workup when using proper diagnostic algorithms 1
- CTPA requires specific contrast timing to optimally opacify pulmonary arteries, which standard chest CT does not provide 1
Diagnostic Algorithm
Step 1: Clinical Probability Assessment
- While not explicitly stated in your question, the presence of dyspnea with elevated D-dimer suggests at minimum intermediate probability 1
Step 2: D-dimer Interpretation
- Your patient already has an elevated D-dimer, which has triggered the need for imaging 1
- The fact that influenza can elevate D-dimer is irrelevant—the test is positive and requires follow-up 1, 2
Step 3: Imaging Selection
- CTPA is indicated as the definitive test 1
- Sensitivity of D-dimer for PE approaches 100%, but specificity is only 20-66%, necessitating confirmatory imaging 3, 4
Alternative Considerations (Lower Priority)
When Lower Extremity Ultrasound Might Be Added
- Compression ultrasound (CUS) of lower extremities can be performed before or alongside CTPA if there are contraindications to CT (renal failure, contrast allergy) 1
- Finding DVT on ultrasound is sufficient to warrant anticoagulation without CTPA 1
- However, this should not delay CTPA in a stable patient without contraindications 1
V/Q Scanning
- Ventilation-perfusion scanning remains an option but is generally reserved for patients with CT contraindications or to reduce radiation in younger patients 1
- Not the first-line choice in most centers where CTPA is readily available 1
Key Clinical Points
- Do not let the influenza diagnosis create false reassurance—PE and respiratory infections can coexist 2
- The diagnostic yield of CTPA in properly selected patients (elevated D-dimer with clinical suspicion) ranges from 8-15% 5, 6
- Negative predictive value of a negative D-dimer is excellent (approaching 100%), but once positive, imaging is mandatory 3, 4
- Studies show CTPA may be overused when ordered without proper clinical assessment, but in your scenario with dyspnea AND elevated D-dimer, it is appropriately indicated 5, 6