Can D-dimer (D-dimer test) be positive in cases of cellulitis of the leg?

D-dimer in Leg Cellulitis: Diagnostic Considerations

Yes, D-dimer can be positive in cases of cellulitis of the leg, but a positive D-dimer alone should not be used to diagnose deep vein thrombosis (DVT) in this context. D-dimer has limited specificity in inflammatory conditions like cellulitis, and additional diagnostic testing is necessary.

D-dimer in Cellulitis: Pathophysiology and Prevalence

• D-dimer levels can be elevated in cellulitis due to the inflammatory process, even in the absence of DVT 1
• In a prospective cohort study of patients with lower limb cellulitis, 74% had elevated D-dimer levels, yet only 0.5% had concurrent ipsilateral DVT 1
• Cellulitis can cause local inflammation that activates the coagulation cascade, leading to fibrin formation and subsequent degradation, resulting in elevated D-dimer levels 2

Diagnostic Approach for Suspected DVT in Cellulitis

• The American Society of Hematology (ASH) guidelines strongly recommend against using a positive D-dimer alone to diagnose DVT regardless of pre-test probability 3
• For patients with cellulitis and suspected DVT, ultrasound imaging is the recommended diagnostic approach rather than relying on D-dimer alone 3
• In patients with intermediate or high pre-test probability for DVT, ASH recommends starting with proximal lower extremity or whole-leg ultrasound 3

Clinical Decision Making Algorithm

1. Assess pre-test probability for DVT using validated clinical decision rules

   • Note that cellulitis may artificially increase Wells score due to overlapping clinical signs 1

2. For low pre-test probability patients:

   • Consider D-dimer testing, but recognize its limited specificity in cellulitis 3
   • If D-dimer negative: DVT is effectively ruled out 3
   • If D-dimer positive: Proceed to ultrasound imaging 3

3. For intermediate or high pre-test probability patients:

   • Proceed directly to ultrasound imaging without D-dimer testing 3
   • If initial ultrasound is negative but clinical suspicion remains high, perform serial ultrasound 3

Special Considerations and Pitfalls

• D-dimer has particularly limited utility in hospitalized patients and certain populations (post-surgical, pregnant) due to high frequency of false positives 3, 4
• Extremely elevated D-dimer levels (>5000 μg/L) should raise concern for serious conditions including DVT, sepsis, or cancer, even in the context of cellulitis 5
• The prevalence of concurrent DVT in patients with uncomplicated cellulitis is very low (0.5%), suggesting that routine DVT investigation in cellulitis patients without other risk factors may be unnecessary 1
• Asymmetric calf swelling >2cm combined with positive D-dimer has better specificity for DVT than either finding alone 6

Management Implications

• In patients with cellulitis and suspected DVT, ultrasound is the definitive diagnostic test 3
• If ultrasound confirms DVT, therapeutic anticoagulation is indicated 4
• For patients with cellulitis without confirmed DVT, standard cellulitis management should continue without anticoagulation 1