How is a deep vein thrombosis (DVT) diagnosed?
It is frequently quoted that half the people who think they have a deep vein thrombosis (DVT) turn out not to have one but have something else instead; and only half the number of deep vein thromboses (DVTs) that occur cause enough symptoms to be investigated.
There are many cases of people who thought that they had merely sprained muscles in their legs and, only years later, found that they had problems with their deep veins due to a previous deep vein thrombosis (DVT) that are not been treated.
The current gold standard test for deep vein thrombosis (DVT) is a colour flow duplex ultrasound scan performed by a specialist who scans veins every day. To perform the test properly, the whole of the leg needs to be scanned, usually in the lying down position (unlike for varicose veins where the patient should be standing).
The quick “three-point test” where the same scanner is used but only in the groin, in the thigh and behind the knee is not sufficient to exclude a deep vein thrombosis (DVT). It is quite possible that a calf vein deep vein thrombosis (DVT) or a short thigh vein deep vein thrombosis (DVT) can be missed using this quick test.
To get an accurate picture, it is essential to scan the main vein from groin the knee, following it all the way down as it curves around the inside of the thigh to the back of the knee, and then to follow each of the three pairs of veins from the back of the knee to the ankle. This takes a lot of expertise and is not a quick procedure.
Some hospitals and clinics use blood tests to look for signs of blood clotting (thrombosis) as a screening test for deep vein thrombosis. However, like all tests, these are not 100% accurate. If the patient has any other trauma, then these tests almost always show a positive result regardless of whether a deep vein thrombosis (DVT) is present or not. In addition, there is always the risk of a negative test despite having a deep vein thrombosis (DVT). Although these blood tests are not the gold standard, they are cheap and can be performed by very unskilled people and as such can help save resources in large hospitals and clinics.
In the past, other tests being used including venograms (xrays with contrast injection), plethysmography and thermal imaging. All of these tests are very inaccurate and really have no place any more in the modern diagnosis of the deep vein thrombosis (DVT) unless colour flow duplex ultrasonography is not available.