DVT - Imaging and Labortory Findings

1. Contrast venography—Although contrast venography remains the gold standard for diagnosing DVT, it has been largely replaced by ultrasonography in most institutions. The advantages of contrast venography include a sensitivity and specificity of nearly 100% and the ability to detect DVTs of the calf, iliac vessels, and inferior vena cava that can be missed by ultrasound. Its primary disadvantages include its invasive nature, use of contrast material, and availability. Additionally, 5-15% of studies performed are technically inadequate.

2. Ultrasonography—Ultrasonography is the most accurate noninvasive study for diagnosing lower-extremity DVT, with a sensitivity of 93-100% and a specificity of 97-100% in detecting proximal DVTs. The limitations of ultrasonography are its ability to detect pelvic and calf DVTs (20% of which will extend into the popliteal vein and thigh).

3. D-Dimer assay—D-dimer is formed when fibrin is degraded by plasmin. The testing for the presence of D-dimer is by latex agglutination (least sensitive), whole blood agglutination (bedside, qualitative), and enzyme-linked immunoassay (ELISA) (most accurate). When combined with ultrasound, the whole blood agglutination and ELISA have an almost 100% negative predictive value.

From Current Diagnosis & Treatment Emergency Medicine - 6th Ed. (2008)