|
Studies have shown that most patients with leg pain who visit a physician do not have deep vein thrombosis (DVT). Since the standard treatment for DVT (e.g., anticoagulants) can be dangerous for people who don’t need it, it is very important that the diagnosis be confirmed before therapy is begun.
The diagnosis of deep vein thrombosis begins with a thorough physical examination. The examination may reveal a “cord” running through the leg, so the physician will massage and feel closely along the entire length of the leg. A thorough medical history is also important. Up to 80 percent of patients with DVT have one or more known risk factors (e.g., inherited blood disorders, long periods of immobility, pregnancy, cancer, surgery).
If the physician still suspects DVT, tests may be performed, including:
- Duplex ultrasound. This noninvasive, common test uses sound waves to visualize the veins of the leg. Test results are displayed on a computer screen so the physician can look for obstructions. It is the most common test used to diagnose DVT, especially first episodes.
- Impedance plethysmography. During this noninvasive test, a blood pressure cuff is inflated around the thigh, restricting blood flow, while the change in blood volume is measured at the calf with electrodes. The blood pressure cuff at the thigh is rapidly deflated so the physician can measure the rate at which the blood flows from the calf and compare this rate to another, healthy limb. This test is particularly helpful to diagnose recurrent episodes of DVT. However, use of the test is limited because it takes a high degree of training to administer it accurately.
- Contrast venography. This invasive test is considered the “gold standard” for detecting DVT. During this test, a contrast medium is injected into the veins that helps the physician see any obstructions. Although this is the most accurate test, it is used less often than ultrasound because it is invasive and may be uncomfortable for the patient. Currently, contrast venography is recommended if ultrasound or impedance plethysmography are unavailable or if the patient cannot withstand them (e.g. because of a cast on a limb).
Studies have also found that test accuracy is increased if physicians first measure the “pretest probability” of a patient having DVT. The most commonly used method to measure pretest probability is to measure a blood substance called D-dimer, a product of fibrin degradation that is elevated among patients with thromboembolism conditions, including DVT. During this standard blood test, blood will be withdrawn, either from the arm or by finger-prick, and sent to a laboratory for analysis.
An elevated D-dimer is not enough to diagnose DVT, but it is enough to warrant further testing. Studies have shown that less than 10 percent of people who had D-dimer levels less than 500 ng/mL were later diagnosed with thromboembolism conditions, including DVT. D-dimer levels may also be elevated because of cancer, recent trauma or surgery.
Finally, physicians are beginning to use two additional tests to diagnose DVT, although both still remain relatively rare. They are:
- Magnetic resonance imaging (MRI). This noninvasive test uses radio waves to visualize the structures inside the body. It may or may not require contrast material (magnetic resonance venography).
- Computed axial tomography scan (CAT scan). This noninvasive test uses an array of x-ray scanners to create three-dimensional images of internal structures on a computer screen. It is only rarely used to diagnose DVT and its use is currently considered experimental.
| 
/doctor_89.jpg "ulcerative colitis tips")
