Should You Order CT Chest for PE with Wells Score 3 and D-dimer 1.68?
Yes, you should order a CT pulmonary angiography (CTPA) for this patient—a Wells score of 3 indicates intermediate clinical probability of PE, and the D-dimer of 1.68 μg/mL (1680 ng/mL) is significantly elevated, mandating imaging regardless of the intermediate probability score. 1
Clinical Probability Assessment
Your patient falls into the intermediate pretest probability category with a Wells score of 3:
- Wells scores are stratified as: low (0-1), intermediate (2-6), or high (≥7) 1
- With intermediate probability (~25% prevalence), the combination of elevated D-dimer requires proceeding directly to imaging 1
D-dimer Interpretation in This Context
The D-dimer of 1.68 μg/mL is significantly elevated and cannot exclude PE:
- This level is 3.4 times the standard cutoff of 500 ng/mL 1
- Even using an age-adjusted cutoff (65 × 10 = 650 ng/mL), this patient's D-dimer of 1680 ng/mL is 2.6 times above the age-adjusted threshold 1, 2
- At this degree of elevation, PE cannot be safely excluded and imaging is mandatory 1
Why D-dimer Cannot Rule Out PE Here
For intermediate clinical probability patients, a positive D-dimer mandates imaging 1:
- D-dimer has high sensitivity (96%) but poor specificity (35%) for VTE 3
- A negative D-dimer can safely exclude PE in low-to-intermediate probability patients, but a positive result requires confirmatory imaging 1
- The negative predictive value of D-dimer only applies when the test is negative, not when elevated 1, 3
Recommended Imaging Approach
Order multidetector CT pulmonary angiography (CTPA) as the definitive test 1:
- CTPA is the preferred imaging modality when available and there are no contraindications to contrast 1
- A negative multidetector CTPA alone can exclude PE in patients with intermediate pretest probability 1
- The 3-month VTE risk after negative CTPA in intermediate probability patients is approximately 1.3% 1
Post-Surgical Context Considerations
The post-cholecystectomy status is relevant:
- Recent surgery (within past month) is a risk factor that contributes to intermediate-to-high clinical probability 1, 4
- Surgery elevates D-dimer levels independent of VTE, but this doesn't change management—imaging is still required with this degree of elevation 3, 5
- Post-surgical patients have higher rates of false-positive D-dimers, but a level of 1680 ng/mL in the setting of intermediate Wells score cannot be dismissed 3, 6
Critical Pitfalls to Avoid
Never use elevated D-dimer alone to diagnose PE—imaging confirmation is always required 1, 3:
- The positive predictive value of D-dimer is only 35-50% due to poor specificity 1
- Many non-thrombotic conditions elevate D-dimer (infection, inflammation, recent surgery, age) 3, 5
Do not skip imaging based on "only moderate" D-dimer elevation:
- D-dimer levels 3-4 times normal (>1.5-2.0 mg/L) are associated with increased mortality risk and warrant aggressive evaluation 7, 5
- This patient's level of 1.68 mg/L falls into this concerning range 7
Do not order D-dimer without first assessing clinical probability—but in this case, you've appropriately calculated the Wells score first 1
Alternative Considerations Only If CTPA Contraindicated
If contrast CT is contraindicated:
- Consider ventilation-perfusion (V/Q) scanning as an alternative 1
- Lower extremity venous ultrasound can identify DVT, which would establish need for anticoagulation without requiring CTPA 1
- However, negative lower extremity ultrasound does not exclude PE 1
Bottom Line Algorithm
For this specific patient: