The ankle brachial pressure index
The ankle brachial pressure index (ABPI) test is widely used to diagnose PAD, as well as assess how well you're responding to treatment.
- while you lie on your back, the GP or practice nurse will measure the blood pressure in your upper arms and ankles using a cuff and a Doppler probe. A Doppler probe uses sound waves to determine the blood flow in your arteries
- after your scan, the GP will divide your blood pressure's second results (from your ankles) by the first results (from your arms)
If your circulation is healthy, the blood pressure in both parts of your body should be exactly or almost the same. This would make the result of your ABPI 1.
However, if you have PAD, the blood pressure in your ankle will be lower because of a reduction in blood supply. This would make the result of the ABPI less than 1.
In some cases, ABPI may be carried out after you run on a treadmill or cycle on an exercise bike. This is to see the effect of physical activity on your circulation.
This is usually carried out in hospital because most GP surgeries do not have the facilities to perform this test.
In most cases, the GP will be able to confirm a diagnosis of PAD by doing a physical examination, asking about your symptoms and checking your ABPI score.
Further testing is usually only required if:
- there's uncertainty about the diagnosis. For example, if you have leg pain but your ABPI score is normal
- you do not fit the expected profile of somebody with PAD – for example, you are younger than 60 and have never smoked
- the restriction of blood supply in your leg is severe enough that treatment, such as surgery, may be required
Additional hospital-based tests that may be carried out include:
- an ultrasound scan – where sound waves are used to build up a picture of arteries in your leg. This can identify where in your arteries there are blockages or narrowed areas
- an angiogram – where a liquid called a contrast agent is injected into a vein in your arm. The agent shows up clearly on a CT scan or MRI scan and produces a detailed image of your arteries
In some cases, the contrast agent may be injected directly into the arteries of your leg and X-rays may be used to produce the images.