From the Research
For a 68-year-old female with low D-dimer but high clinical suspicion for DVT, the next step should be to proceed with compression ultrasound imaging despite the negative D-dimer result. D-dimer has high sensitivity but limited specificity, and in patients with high clinical probability of DVT, a negative D-dimer cannot reliably exclude thrombosis 1. The ultrasound should focus on the proximal deep veins of the symptomatic leg, particularly the popliteal and femoral veins. If the initial ultrasound is negative but clinical suspicion remains high, either serial ultrasound testing (repeating in 5-7 days) or additional imaging such as complete leg ultrasound or venography should be considered.
While awaiting definitive diagnosis, it would be reasonable to administer prophylactic anticoagulation with low molecular weight heparin (such as enoxaparin 40mg subcutaneously daily) or fondaparinux (2.5mg subcutaneously daily) 2. This approach balances the risk of missing a potentially dangerous DVT against unnecessary full-dose anticoagulation. The patient should also be advised to monitor for worsening symptoms such as increased pain, swelling, or development of chest pain or shortness of breath which could indicate pulmonary embolism.
It's worth noting that recent evidence suggests that the administration of direct oral anticoagulants (DOACs) such as rivaroxaban may reduce the sensitivity and increase false negative results of D-dimer testing 3. Therefore, if the patient is already on DOACs, the D-dimer result should be interpreted with caution. However, in this case, since the D-dimer was already low, proceeding with compression ultrasound imaging is still the most appropriate next step.
Key considerations in the management of this patient include:
- High clinical suspicion for DVT despite low D-dimer
- Need for compression ultrasound imaging to confirm or rule out DVT
- Potential for serial ultrasound testing or additional imaging if initial ultrasound is negative
- Consideration of prophylactic anticoagulation while awaiting definitive diagnosis
- Monitoring for worsening symptoms that could indicate pulmonary embolism.