For a patient with a recent diagnosis of Deep Vein Thrombosis (DVT) in the femoral vein, currently being treated with Eliquis (apixaban), will D-dimer testing be an accurate method for diagnosing a potential Pulmonary Embolism (PE)?

D-Dimer Testing in a Patient with Confirmed DVT and Suspected PE

D-dimer testing will NOT be useful for diagnosing PE in your patient with confirmed femoral DVT because the D-dimer is already elevated from the existing DVT, making it impossible to distinguish whether an elevated result is from the known DVT, a new PE, or both. 1, 2

Why D-Dimer Cannot Help in This Clinical Scenario

• D-dimer is a degradation product of cross-linked fibrin that is elevated in any active venous thromboembolism, including both DVT and PE 1, 3
• The American College of Chest Physicians explicitly states that D-dimer levels are elevated in patients with DVT, and this elevation persists during active thrombosis 1
• Your patient already has a confirmed source of elevated D-dimer (the femoral DVT), which fundamentally eliminates the test's diagnostic utility for detecting a concurrent PE 2, 4
• The American Society of Hematology emphasizes that D-dimer is only useful as a "rule-out" test when negative in patients without known thrombosis - it cannot differentiate between different thrombotic sources 2

The Correct Diagnostic Approach for Your Patient

Proceed directly to CT pulmonary angiography (CTPA) without obtaining D-dimer testing. 1, 2

Imaging-Based Algorithm

• For patients with confirmed DVT and clinical suspicion of PE, the European Society of Cardiology and American Society of Hematology recommend proceeding directly to definitive imaging with CTPA 1
• CTPA has sufficient sensitivity and specificity to diagnose or exclude PE as a standalone test in this clinical context 1
• The American Society of Hematology explicitly recommends against using D-dimer as a subsequent test following confirmed thrombosis, as it provides no additional diagnostic value 1, 2

Clinical Probability Assessment Still Matters

• Even though D-dimer is not useful, assess your patient's clinical probability of PE using validated scores (Wells or Geneva) to guide urgency and pre-test probability 1, 2
• Signs suggesting PE include: new dyspnea, chest pain, hemoptysis, tachycardia >100 bpm, or hypoxemia 1
• If your patient has high clinical probability features (hemodynamic instability, severe hypoxemia), consider echocardiography to assess for right ventricular strain while arranging urgent CTPA 1

Critical Pitfalls to Avoid

• Never delay imaging to obtain D-dimer in a patient with known DVT - this wastes time and provides no diagnostic information 1, 2
• The American Society of Hematology warns that pathways attempting to use positive D-dimer results for diagnosis yield unacceptably high false-positive rates and should never be employed 1, 2
• Do not be falsely reassured if D-dimer happens to be "only moderately elevated" - the degree of elevation does not reliably distinguish DVT alone from DVT plus PE 1, 2

Regarding the Eliquis Treatment

• The fact that your patient just started Eliquis does not significantly affect D-dimer levels in the acute setting (first 24-48 hours), but this is irrelevant since D-dimer should not be used regardless 1
• Continue therapeutic anticoagulation with Eliquis while pursuing PE diagnosis, as the treatment for DVT and PE is identical (therapeutic anticoagulation) 5
• If PE is confirmed on CTPA, no change in anticoagulation regimen is needed - continue the same Eliquis dosing 5

Summary of the Diagnostic Pathway

1. Skip D-dimer entirely - it will be elevated from the DVT and cannot provide diagnostic information 1, 2
2. Assess clinical probability of PE using Wells or Geneva score to determine urgency 1, 2
3. Proceed directly to CTPA as the definitive diagnostic test 1, 2
4. Continue therapeutic anticoagulation with Eliquis throughout the diagnostic workup 5