Diagnostic Approach

Clinical diagnosis of DVT lacks sensitivity and specificity. Only about 50% of confirmed DVT cases present with classic unilateral leg swelling, pain, erythema, and positive Homan’s sign. Objective testing is required to accurately diagnose DVT.

• Contrast venography is the gold standard for DVT diagnosis but is rarely used now due to its invasive nature. It allows evaluation of the entire deep venous system.
• Compression ultrasound is the preferred initial test for suspected lower extremity DVT. It is noninvasive, low cost, and portable. Ultrasound evaluates compressibility of the common femoral, femoral, popliteal, and calf veins. Lack of complete compressibility indicates DVT. Ultrasound has 95% sensitivity and 96% specificity for symptomatic proximal lower extremity DVT. Its accuracy is lower for asymptomatic or distal DVT.
• If initial ultrasound is negative but pretest probability is moderate or high, repeat ultrasound in 5-7 days to detect evolving DVT. Up to 2% more DVT cases are identified on repeat ultrasounds.
• D-dimer blood test has high sensitivity but low specificity. A negative D-dimer in low-risk patients can exclude DVT.
• MRI direct thrombus imaging is sometimes used for suspected pelvic DVT if ultrasound is inconclusive.
• Impedance plethysmography assesses venous outflow obstruction but has fallen out of favor due to lower accuracy.

In summary:

• Ultrasound: Initial test of choice for suspected lower extremity DVT.
• Serial ultrasounds: Increase sensitivity for diagnosing evolving DVT.
• D-dimer: Helps exclude DVT when negative in low-risk patients.
• Venography: Gold standard but rarely used due to invasive nature.
• Compression ultrasound and clinical correlation are key for accurate DVT diagnosis.