Wet gangrene of lower limb is the clinical manifestation of femoral bruise, an important sign of lower limb venous thrombosis, and it is the most serious type of DVT in clinic, mainly because of extensive iliac-femoral vein occlusion, the whole lower limb venous system is almost in the state of obstruction, the venous pressure is extremely high, the bruise is serious, and the lower limb appears highly edematous, and then arterial spasm occurs, and the limb blood supply is insufficient. Clinical deep vein thromboembolism (DVT) of the lower extremities can not be diagnosed only by clinical manifestations, but also need to be confirmed by auxiliary examination, today for you to inventory the auxiliary examination methods of DVT. 1, plasma D-dimer measurement is often used in the first choice of screening for venous thrombosis, but it can not confirm the diagnosis. Because D-dimer test is highly sensitive, but the specificity is poor, and it will be elevated in the case of malignant tumors, trauma, surgery, infection and so on. D-dimer negative predictive value (<500μg/L) is used to exclude acute pulmonary embolism and DVT, and when D-dimer becomes positive (>500μg/L), further examination is required. Doppler ultrasonography, with high sensitivity and accuracy and non-invasive diagnosis, is the preferred method for DVT diagnosis. Spiral CT venography is more accurate and has more advantages, but the cost is high. 4.Magnetic resonance venography It can accurately show iliac, femoral and popliteal vein thrombosis, but cannot satisfactorily show calf vein thrombosis. No contrast agent is required. 5, Venography High accuracy, not only can effectively determine the presence or absence of thrombus, thrombus site, scope, formation time and collateral circulation, and often used to identify the diagnostic value of other methods, but because it is an invasive examination, it is not suitable as the first choice, and is only used for patients with negative non-invasive examination and high suspicion of venous thrombosis.