Deep vein thrombosis (DVT) - Diagnosing deep vein thrombosis

If you think that you may have deep vein thrombosis (DVT), see your GP as soon as possible. 

Your GP will ask you about your medical history and your symptoms. However, it can be difficult to diagnose DVT from symptoms alone, so your GP may recommend one of the following tests:

D-dimer test

A specialised blood test known as the D-dimer test is used to detect pieces of blood clot that have been broken down and are loose in your bloodstream. The larger the number of fragments found, the more likely it is that you have a blood clot in your vein.

However, the D-dimer test is not always reliable. Blood clot fragments can increase after an operation or injury, or if there is inflammation in your body (when your immune system reacts to an infection or disease). This means that additional tests, such as an ultrasound scan, need to be performed to confirm DVT.

If the D-dimer test is negative, it rules out the possibility of a DVT in up to 97% of cases.

Ultrasound scan

An ultrasound scan can be used to detect clots in your veins. A special type of ultrasound known as a Doppler ultrasound can also be used to find out how fast the blood is flowing through a blood vessel. This helps doctors identify when blood flow is slowed or blocked, which could be caused by a blood clot.

Venogram

If the results of a D-dimer test and ultrasound scan cannot confirm a diagnosis of DVT, a venogram might be used. 

A special dye is injected into a vein in your foot, which travels up the blood vessels of your leg. An X-ray is taken to see the dye. If there is a blood clot in your leg, the dye will not be able to flow round it and will show up as a gap in your blood vessel.

Glossary

Ultrasound

Ultrasound scans are a way of producing pictures of inside the body using sound waves.

Ultrasound scan

Blood vessel

Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.

Vein

Veins are blood vessels that carry blood from the rest of the body back to the heart.

X-ray

An X-ray is a painless way of producing pictures of inside the body using radiation.

Blood

Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.

Blood test

During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.