Deep Venous Thrombosis: Diagnosis

Diagnostic procedures must differentiate DVT from other disorders that cause similar symptoms. Unilateral extremity swelling may be due to hemorrhage, muscle rupture, ruptured popliteal cyst, and lymphedema. Limb pain can result from arthritis, tendonitis, nerve compression, traumatic injuries, and fractures.

Imaging

Duplex venous ultrasonography is the most common initial diagnostic method for DVT. A thrombus can be detected by direct visualization, or by inference when the vein fails to collapse when compressed.

Magnetic resonance imaging (MRI) offers high sensitivity and specificity for suspected thromboses of the venae cavae or pelvic veins, conditions that other imaging modalities often miss. MRI and magnetic resonance angiography (MRA) also are highly accurate in detecting PE.

Impedance plethysmography measures changes in venous capacity during movement or compression. Venous obstruction alters the venous capacity that occurs following inflation or deflation of the cuff. This test can identify obstruction in areas typically missed by ultrasound (eg, inferior vena cava).

Venography works by injecting a contrast medium into a superficial vein of the foot and moving it to the deep veins by a system of tourniquets. A filling defect or the absence of filling in the deep veins is required to make the diagnosis. Because venography is time consuming and requires technical expertise, it has been replaced almost entirely by noninvasive methods.

Electrocardiogram (ECG) and chest x–ray have limited sensitivity and specificity for PE, and most often are used to exclude other causes of symptoms. However, unusual but useful findings such as ECG signs of right ventricular overload or chest x–ray evidence for pulmonary pruning or infarction, may contribute to diagnosis.

Ventilation–perfusion (V/Q) scan is used to identify PE. Newer and simpler imaging modalities, such as the helical (spiral) CT scan, MRI, and MRA are replacing V/Q scans in many situations. In some cases, CT pulmonary angiography is used after, or instead of, these noninvasive tests.

2D echocardiogram is a rapid and simple procedure for PE diagnosis. Occasionally, the embolus may be seen in transit through the right ventricle or in the proximal pulmonary arteries, and not uncommonly signs of acute right ventricular overload will greatly assist diagnosis and risk stratification. Echocardiography also may identify other etiologies for symptoms in patients with suspected PE.

Blood tests

Arterial blood gas determination is not sensitive or specific for the presence of PE, but severe hypoxemia may indicate massive embolism and affect treatment decisions.

D–dimer test. D–dimer is an end product of the degradation of fibrin clots. A positive result suggests the presence of DVT or PE, but the test has poor specificity (about 50%). Sensitivity is quite high (94% to 98%), so a normal D–dimer level is strong, but not absolute, evidence against the presence of thrombus. Combination screening with D–dimer and at least one imaging modality may be most effective.^1,2