Is D-dimer (D-dimer test) positive in Deep Vein Thrombosis (DVT)?

D-dimer Testing in Deep Vein Thrombosis

D-dimer is typically positive in patients with Deep Vein Thrombosis (DVT), with a high sensitivity of 96% but low specificity of 35%, making it an excellent "rule-out" test but poor "rule-in" test for DVT. 1

Diagnostic Value of D-dimer in DVT

• D-dimer has high sensitivity (96%, 95% CI: 92-98%) for DVT, meaning a negative result can effectively rule out DVT in patients with low clinical probability 2
• D-dimer specificity is low (35%, 95% CI: 28-43%), resulting in many false positives, which limits its value as a confirmatory test 2
• The negative predictive value of D-dimer for venous thromboembolism can reach 100% when using appropriate cutoff values (0.5 μg/ml for VIDAS D-dimer) 3
• D-dimer levels are significantly higher in patients with thrombosis compared to those without thrombosis 3

Clinical Application in Suspected DVT

• For patients with low clinical probability of DVT (≤10%), a negative D-dimer result effectively rules out DVT without the need for additional testing 2, 1
• The American Society of Hematology recommends starting with a highly sensitive D-dimer test in patients with low clinical probability, and if negative, no further testing is required 2, 1
• For patients with intermediate or high clinical probability, D-dimer testing alone is insufficient and imaging studies are necessary 2, 1
• Never use a positive D-dimer alone to diagnose DVT - confirmation with imaging is always required 1

Diagnostic Algorithm Based on Clinical Probability

Low Clinical Probability (≤10%):

• Start with highly sensitive D-dimer test 2
• If D-dimer negative: No DVT, no further testing needed 2
• If D-dimer positive: Proceed to imaging (proximal or whole-leg ultrasound) 2

Intermediate Clinical Probability (~25%):

• Consider proximal or whole-leg ultrasound 2
• Alternatively, start with D-dimer if prevalence is ≤15% 2
• If D-dimer negative: No DVT 2
• If D-dimer positive: Proceed to ultrasound 2

High Clinical Probability (≥50%):

• Proceed directly to proximal or whole-leg ultrasound without D-dimer testing 2
• Serial ultrasound if initial ultrasound is negative and no alternative diagnosis 2

Limitations and Special Considerations

• D-dimer has limited utility in hospitalized patients and certain populations (post-surgical, pregnant) due to high frequency of positive results regardless of DVT status 2, 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
• D-dimer as a stand-alone test may be safe for excluding proximal DVT with a failure rate of only 0.6% (95% CI: 0.1%-1.8%) for proximal DVT 4
• Different D-dimer assays have varying sensitivities and specificities, with some assays showing sensitivities as low as 63% 5

Common Pitfalls to Avoid

• Relying solely on a positive D-dimer to diagnose DVT without confirmatory imaging 1
• Using D-dimer testing in patients where results are likely to be positive regardless of DVT status (hospitalized, post-surgical, pregnant patients) 1
• Performing additional testing following a negative proximal or whole-leg ultrasound in a low-risk population 1
• Using D-dimer as a stand-alone test without considering clinical probability 6
• Failing to recognize that D-dimer testing is not necessary when DVT diagnosis is already established, as it has no role in monitoring treatment 7

In conclusion, while D-dimer is typically positive in DVT patients, its primary value is in excluding DVT when negative in low-risk patients rather than confirming DVT when positive.