Deep Vein Thrombosis
Examinations and Tests
Assessing your risk
Deep vein thrombosis may first be suspected after a medical history and physical examination. The information gathered from these initial tests will help your doctor determine whether your risk level for having deep vein thrombosis is low, medium, or high. Your risk level will help your doctor decide the appropriate testing for deep vein thrombosis.
Most frequently used tests
Ultrasound is the main test used to help diagnose deep vein thrombosis. It creates a picture of the flow of blood through the veins. The testing sequence for deep vein thrombosis is based on your risk level and results from your initial ultrasound. If additional testing is needed, it usually consists of:
- Repeat ultrasounds, usually done a few days to a week apart. This is also called serial testing.
- Venogram. In venography, a contrast dye is injected into the veins to make them visible on an X-ray picture.
Venography is useful if ultrasound testing does not provide a clear diagnosis. Ultrasound tests do not consistently provide accurate results in the veins of the calves. Although blood clots in the deep veins of the calf are not usually dangerous, these clots may eventually extend above the knee, where they are more dangerous. Clots that occur in the upper leg veins put a person at high risk for developing pulmonary embolism. For this reason, repeated ultrasounds, venography, or other tests may be useful in identifying blood clots that may have been missed by ultrasound.
Additional tests
Additional tests may be used when ultrasound results are unclear and venography is not available or results do not provide a clear diagnosis. These tests may help diagnose or exclude a blood clot in the leg but are not frequently needed. Additional tests may include:
- D-dimer test. This blood test is sometimes used either before ultrasound or after ultrasound if the results are not clear to rule out the possibility of deep vein thrombosis in low-risk cases.6
- Magnetic resonance image (MRI).
- Computed tomography (CT) scan.
If you are treated with anticoagulant medications, you may need periodic blood tests to monitor the effects of the anticoagulant on the blood. Blood tests include:
- Activated partial thromboplastin time (APTT) to monitor treatment with standard or unfractionated heparin.
- Prothrombin time (PT) to monitor treatment with warfarin (Coumadin).
If you are suspected of having pulmonary embolism, you may have a lung scan, a spiral CT scan, or a pulmonary angiogram. For more information, see the topic Pulmonary Embolism.
Early Detection
Special blood tests may help identify inherited blood-clotting abnormalities that can increase your risk of forming blood clots. However, screening for these factors is not routinely done and is somewhat controversial.
In general, screening is sensible if you have or have had one or more of the following:7
- A blood clot in a vein that has no clear cause
- A blood clot at age 45 or younger
- One or more immediate family members (mother, father, brother, or sister) who have had a blood clot in a vein. A family history of blood clots in arteries does not increase your risk of having a blood clot in a vein.
- A blood clot in a vein at an unusual location, such as the gastrointestinal region, the brain, or the arms
Some health professionals believe that more routine screening could help prevent deep vein thrombosis in people who have an increased risk and are in a high-risk situation (such as upcoming surgery) because preventive measures can then be taken.
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| Author: | Merrill Hayden Nancy Reid | Last Updated: April 5, 2006 |
| Medical Review: | Adam Husney, MD - Family Medicine Jeffrey S. Ginsberg, MD - Hematology | |
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