How is deep vein thrombosis (DVT) diagnosed?
The diagnosis of superficial thrombophlebitis usually is made by the doctor at the bedside of the patient, based upon history, potential risk factors present, and findings from the physical examination. Further risk stratification tools may include scoring systems that can help decide whether a DVT is likely.
If the probability of a DVT is low, a D-dimer blood test may be ordered.
- If the D-dimer is negative, then it is unlikely that a DVT is the diagnosis.
- If the D-dimer is elevated, then the possibility of a DVT exists and an imaging study, usually ultrasound, is required to look for the DVT
- Ultrasound is the standard method of diagnosing the presence of a deep vein thrombosis.
- The ultrasound technician may be able to determine whether a clot exists, where it is located in the leg or arm, and how large it is. It also may be possible to know whether the blood clot is new or chronic. If necessary, ultrasounds may be compared over time to see whether a clot has grown or resolved.
- Ultrasound is better at "seeing" the veins above the knee as compared to the small veins below the knee joint.
- Clots in the chest or pelvis may not be identified on ultrasound.
D-dimer is a blood test that may be used as a screening test to determine if a blood clot exists. D-dimer is a chemical that is produced when a blood clot in the body gradually dissolves. The test is used as a positive or negative indicator. If the result is negative, then in most cases no blood clot exists. If the D-dimer test is positive, it does not necessarily mean that a deep vein thrombosis is present since many situations will have an expected positive result. Any bruise or blood clot will result in a positive D-dimer result (for example, from surgery, a fall, in cancer or in pregnancy). For that reason, D-dimer testing must be used selectively.
Other tests for DVT
- Venography, injecting dye into the veins to look for a thrombus, is not usually performed anymore and has become more of a historical footnote.
- Other blood testing may be considered based on the potential cause for the deep vein thrombosis.