Initial Laboratory Tests for Suspected Deep Vein Thrombosis (DVT)
The initial laboratory evaluation for suspected DVT should include a D-dimer test combined with clinical pretest probability assessment to guide the diagnostic approach. 1
Clinical Probability Assessment
- Clinical assessment should stratify patients into low, moderate, or high pretest probability of DVT using a validated clinical model 1
- This assessment guides the selection and interpretation of subsequent diagnostic tests 1
Diagnostic Algorithm Based on Pretest Probability
Low Pretest Probability
- Begin with a moderately sensitive (Grade 2C) or highly sensitive (Grade 2B) D-dimer test 2
- If D-dimer is negative, no further testing is needed as DVT is ruled out 2, 1
- If D-dimer is positive, proceed to proximal compression ultrasound (CUS) 2
Moderate Pretest Probability
- Begin with a highly sensitive D-dimer test (Grade 2C) or proceed directly to ultrasound 2, 1
- If D-dimer is negative, no further testing is needed 2, 3
- If D-dimer is positive, proceed to proximal CUS 2
High Pretest Probability
- Proceed directly to proximal CUS or whole-leg ultrasound 2, 1
- D-dimer testing is less useful in this population due to high likelihood of positive results 1
Special Considerations
- D-dimer may be falsely elevated in pregnancy, inflammation, malignancy, and advanced age 1, 4
- Initial ultrasound testing is preferred over D-dimer in patients with comorbid conditions likely to cause elevated D-dimer levels 2, 1
- For pregnant patients, initial evaluation with proximal CUS is recommended over D-dimer testing 2, 1
- For suspected upper extremity DVT, initial evaluation with combined modality ultrasound (compression with either Doppler or color Doppler) is suggested 2
Pre-Therapy Testing When DVT is Confirmed
- Complete blood count with platelet count to establish baseline values 5
- Coagulation profile including prothrombin time, international normalized ratio, and activated partial thromboplastin time 5
- Comprehensive metabolic panel to assess kidney and liver function, which will influence anticoagulant selection and dosing 5
Common Pitfalls to Avoid
- Failing to check baseline laboratory values before initiating anticoagulation can lead to complications 5
- Overlooking the need for iliac vein imaging in patients with extensive leg swelling when proximal ultrasound is negative 1, 5
- Relying solely on D-dimer without considering clinical probability can lead to unnecessary ultrasound testing 3, 6
- Using latex D-dimer assays, which have lower sensitivity than ELISA techniques 7