D-Dimer Testing in Suspected Deep Vein Thrombosis
D-dimer testing should be used as the initial test for patients with low clinical probability of DVT, followed by ultrasound imaging if positive, but should not be used alone to diagnose DVT. 1
Appropriate Use of D-Dimer Testing
- D-dimer testing is recommended as the first-line test in patients with low clinical probability/prevalence (≤10%) of deep vein thrombosis (DVT) 1
- A negative D-dimer result in a patient with low clinical probability effectively rules out DVT without the need for additional testing 1
- D-dimer has a high sensitivity (96%) but low specificity (35%) for DVT, making it valuable as an exclusionary test but not as a diagnostic test 1
- D-dimer testing should always be used in conjunction with clinical probability assessment using validated clinical decision rules 1
Clinical Decision Algorithm
For Patients with Low Clinical Probability of DVT:
- Start with a highly sensitive D-dimer test 1
- If D-dimer is negative: No DVT; no further testing required 1
- If D-dimer is positive: Proceed to proximal compression ultrasound or whole-leg ultrasound 1
For Patients with Intermediate or High Clinical Probability of DVT:
- For intermediate probability: Consider whole-leg ultrasound 1
- For high probability: Proceed directly to proximal compression ultrasound or whole-leg ultrasound 1
- D-dimer should not be used alone to diagnose DVT regardless of clinical probability 1
Important Limitations and Considerations
- D-dimer has limited utility in hospitalized patients and certain populations (post-surgical, pregnant) due to high frequency of positive results with standard thresholds 1
- Age-adjusted D-dimer cutoffs (age × 10 mg/L) should be considered for outpatients older than 50 years to improve specificity while maintaining safety 1
- Using D-dimer testing in appropriate patients can significantly reduce the need for ultrasound imaging (from 1.34 to 0.78 tests per patient in one study) 2
- The failure rate of D-dimer as a stand-alone test is approximately 1.8% overall and 0.6% for proximal DVTs, highlighting why it should not be used alone for diagnosis 3
- D-dimer testing requires a highly sensitive assay; latex agglutination assays are relatively insensitive and should not be used 4
Pitfalls to Avoid
- Never use a positive D-dimer alone to diagnose DVT - confirmation with imaging is always required 1
- Avoid ordering D-dimer in patients where results are likely to be positive regardless of DVT status (hospitalized, post-surgical, pregnant patients) 1
- Be aware that D-dimer tests may have different intended uses by manufacturer - some are approved for VTE exclusion while others are only for aid to diagnosis 5
- D-dimer is sometimes ordered for unexpected indications (stroke, dissection, ECMO) where its utility has not been established 6
- Do not perform additional testing following a negative proximal or whole-leg ultrasound in a low-risk population 1