Testing for Clots Throughout the Body
Diagnosing deep vein thrombosis and pulmonary embolism may be difficult as the signs and symptoms associated with these disorders are not unique to these conditions. For example, leg pain and swelling or chest pain and shortness of breath may have other causes. As a result, testing is needed to confirm the diagnosis.
Venography and pulmonary angiography remain the gold standards for diagnosis of deep vein thrombosis and pulmonary embolism respectively; however, these tests are now being increasingly replaced by less invasive and less expensive procedures. Three types of imaging tests may be used to diagnose clots in veins.
RADIO LABEL TESTS
Radioactive fibrinogen leg scanning is moderately sensitive and specific for clots in the calf and popliteal veins, but less sensitive for superficial clots in the femoral or iliac veins.
The AcuTect venogram test is a synthetic radiochemical that binds to a protein found on activated platelets. The AcuTect venogram is used to diagnose acute venous clots in the lower extremities of patients with signs and symptoms of such clots. The AcuTect appears to detect acute, but not chronic, clots in the veins.
ULTRASOUND TESTS
The doppler-augmented ultrasound and impedance plethysmography technique are sensitive to proximal clots that cause blockages. Impedance plethysmography does not detect calf vein clots or proximal vein clots that do not block the blood vessel.
Doppler ultrasonography is the most widely available noninvasive test for deep vein thrombosis. Doppler ultrasonography has become the dominant test since the 1980s and has largely replaced impedance plethysmography for noninvasive testing.
X-RAY AND COMPUTED TOMOGRAPHY TESTS
Venography testing can detect clots in both calf and proximal veins.
V/Q scanning may be used as a one-step method to diagnose pulmonary embolism in patients with a normal chest radiograph. In patients with an abnormal chest radiograph, V/Q scanning should be used in combination with helical spiral computed tomography testing. V/Q scans tend to be used mainly to exclude rather than confirm pulmonary embolism. V/Q scanning is able to show small clots–and this ability is enhanced by single photon emission computed tomography.
The helical spiral computed tomography technique is very effective in diagnosing clinically important pulmonary embolism and a large number of alternative diagnoses in patients with symptoms who have undergone a V/Q scan. This is an accurate method for detecting and excluding most types of pulmonary embolism.
Laboratory testing is another method of diagnosis