What is ankle-brachial index?
The ankle-brachial index (ABI) is a test used to determine the presence and severity of peripheral artery disease (PAD) in the legs. The test compares the blood pressure in the ankle to the blood pressure in the arm. ABI is calculated by dividing the systolic blood pressure in the ankle by the systolic blood pressure in the arm. The test is performed by a healthcare provider and is non-invasive.
Why is it done?
The ABI test is done to determine the presence and severity of PAD in the legs. PAD is a condition in which the blood vessels in the legs become narrowed or blocked, reducing blood flow to the legs and feet. This can lead to symptoms such as leg pain or cramping, fatigue, and difficulty walking. In severe cases, PAD can lead to amputation of the affected limb.
The ABI test is a simple, non-invasive way to detect PAD early and determine the best course of treatment for the patient. The test can also be used to monitor the effectiveness of treatment for PAD.
The test is often used as a screening tool for people who are at high risk for PAD, such as smokers, people with diabetes, or those with a family history of the condition. It is also commonly done for people who have symptoms such as leg pain or cramping, fatigue, or difficulty walking. By identifying PAD early, the ABI test can help prevent serious complications such as amputation and improve the patient’s quality of life.
The test is a simple, non-invasive procedure that can be performed in a doctor’s office or clinic. The test typically takes about 15-20 minutes to complete.
Here are the steps to perform the test:
1. The patient lies down and the healthcare provider will take the blood pressure in both the arm and ankle using a blood pressure cuff and a Doppler ultrasound.
2. The systolic blood pressure (the higher number) is measured in both the arm and ankle.
3. The ABI is calculated by dividing the systolic blood pressure in the ankle by the systolic blood pressure in the arm.
4. The test is usually done on both legs, and the ABI is calculated for each leg.
A normal ABI is between 0.9 and 1.3. A value less than 0.9 is indicative of PAD. In some cases, the test may be repeated after exercise or with the use of a medication to open the blood vessels.
The ABI is calculated by dividing the systolic blood pressure in the ankle by the systolic blood pressure in the arm. The systolic blood pressure is the higher number in a blood pressure reading and indicates the pressure in the vessels when the heart beats.
Here is an example of how to calculate the ABI:
- If the systolic blood pressure in the right ankle is 120 mm Hg and the systolic blood pressure in the right arm is 140 mm Hg, the ABI would be calculated as: ABI = 120 mm Hg / 140 mm Hg = 0.86
It is important to note that ABI test is not a substitute for other diagnostic tests such as angiography, but can be helpful in identifying patients who should undergo further evaluation.