What blood tests are commonly done in a suspected case of Deep Vein Thrombosis (DVT)?

Blood Tests in Suspected DVT

D-dimer is the primary blood test used in suspected DVT, with its role determined by clinical pretest probability—it should never be used as a stand-alone test in high-probability patients but effectively excludes DVT when negative in low-to-moderate probability patients. 1, 2

D-Dimer Testing Strategy

The American College of Chest Physicians recommends D-dimer testing based on pretest probability assessment: 3, 1

• Low pretest probability patients: Start with D-dimer testing (moderately or highly sensitive assay). A negative result excludes DVT without further testing. A positive result requires proximal compression ultrasound. 1, 2

• Moderate pretest probability patients: Either highly sensitive D-dimer or proceed directly to ultrasound. A negative highly sensitive D-dimer excludes DVT. 1, 2

• High pretest probability patients: Proceed directly to imaging (proximal compression ultrasound or whole-leg ultrasound). Do not use D-dimer as a stand-alone test in this population. 1, 2

D-Dimer Test Characteristics

• Sensitivity: ELISA-based D-dimer assays demonstrate 96.8% sensitivity for DVT, making them highly effective for ruling out disease when negative (cut-off typically <500 ng/mL). 4

• Specificity: D-dimer has low specificity (35-45%), meaning elevated levels occur in many conditions besides DVT and cannot confirm the diagnosis. 4

• Negative predictive value: A negative D-dimer combined with low pretest probability has a negative predictive value of 99% for DVT. 5, 6

Critical Limitations and Pitfalls

Avoid D-dimer testing in patients with conditions that cause false elevation: 2

• Pregnancy 1
• Active malignancy 2
• Infection or inflammation 2
• Advanced age 2
• Recent surgery or trauma 5

In these populations, start directly with compression ultrasound rather than D-dimer testing. 2

Special Populations

Upper extremity DVT: D-dimer has 92% sensitivity and 98% negative predictive value for upper extremity DVT, though combined-modality ultrasound remains the preferred initial test. 7, 8

Pregnant patients: The American College of Chest Physicians recommends starting with proximal compression ultrasound over D-dimer testing due to physiologically elevated D-dimer levels during pregnancy. 3, 2

Recurrent DVT: A negative highly sensitive D-dimer excludes recurrent DVT without further testing. 3, 2

Other Blood Tests

No other blood tests are routinely recommended for diagnosing suspected DVT. 3 While baseline coagulation studies (PT/INR, aPTT) and complete blood count may be ordered before initiating anticoagulation, these are for treatment planning rather than diagnosis. 1

Practical Algorithm

1. Assess clinical pretest probability (Wells score or clinical gestalt) 1, 2
2. Low probability: Order D-dimer → if negative, DVT excluded; if positive, order ultrasound 1
3. Moderate probability: Order highly sensitive D-dimer or proceed to ultrasound → if D-dimer negative, DVT excluded 1
4. High probability: Skip D-dimer, proceed directly to ultrasound imaging 1, 2

Never rely on D-dimer alone in high-risk patients, as the negative predictive value drops to 85.7% in this population compared to 99.5% in low-risk patients. 5