The ankle-brachial index, ankle-arm index, ankle-arm ratio, or the Winsor Index (first described in 1950 by Winsor) is a quick, non-invasive, inexpensive technique used widely to check the peripheral arterial disease (PAD). It assesses the severity of arterial insufficiency of arterial narrowing during walking.
As the blood pressure of arms is an indicator for the general blood pressure of the body, but when blood go farther in the body through the arteries the pressure changes according to the condition of the patient’s arteries and the general health also resting and exercising situations will show different changes in reading.
The ankle-brachial index ABI is measured by dividing the ankle systolic pressure by brachial systolic pressure.
Risk factors for PAD, such as:
- History of tobacco use
- High blood pressure
- High cholesterol
- Restricted blood flow (atherosclerosis) in other parts of your body.
- Patients with confirmed or suspected DVT, because of the possibility of breaking of the thrombus.
- Severe leg pain.
Hand-held Doppler, or hand-held ultrasound device that's pressed on your skin
- Rest for minutes before the measurements 10-30 minutes like normal blood pressure taken during normal visits.
- Loose, comfortable clothes will be a better choice for easily wearing the inflated cuff on the upper arm.
- Avoid nicotine/ smoking as it shows an increase in the peripheral systolic pressure resulting in elevated ABI value.
- Supported, comfortable position, and avoid limb movement during measurements.
- The supine position is the position of choice as the sitting position shows about 0.3 increase in the ABI,
The same procedures as in the measurement of normal blood pressure, with the patient in rested position, it is better to measure the brachial pressure before the ankle pressure:
1- Place the cuff around the patient's arm, use the hand-held ultrasound device or hand doppler and press against the skin at the level of the brachial artery in the arm in order to hear the waves of the systolic pressure, repeat on the other arm and record the highest measurement.
2- Place the cuff around the lower leg and use the hand-held ultrasound device to hear the waves of the systolic pressure at two levels :
- Dorsalis pedis, which is a branch from the anterior tibial artery, it is located between the tibialis anterior and extensor hallucis longus
- Posterior tibial pulse, that is behind the lateral malleoli.
3- Record the highest pulse between two measurements of dorsalis pedis and posterior tibial arteries.
4- The ankle-brachial index calculated by dividing the highest value of ankle systolic pressure between the two arteries by the highest brachial pressure between two sides.
5- Repeat the ankle measurement for the other leg in order to calculate its ABI.
6- The normal ABI is between 0.90 and 1.30, below indicate PAD, above may be a sign of arterial calcification.
The normal range is between 0.90 and 1.30. below 0.8 means there is a difficulty of blood flow to the foot and lower limb.
Below 0.7 means severe peripheral artery disease PAD and the patient may develop ulcer and gangrene.
Above the normal level, 1.30 is a sign of calcification of arterial walls that may happen in case of diabetic patients, chronic kidney disease, in this situation you need to measure the ankle pressure at distal digital arteries that is less likely to develop or be calcified
- In normal healthy people, there is a slight decrease in ABI if measured immediately after lower limb exercises due to the decreased ankle systolic pressure because of vasodilation during lower limb exercises, and return to normal within about 3 min after rest.
- There is more decrease in ankle pressure after walking in case of moderate occlusive PAD specifically in the proximal vessels.
- The ABI has a high sensitivity, but these results came from one single study which may be included participants with critical limb ischemia or diabetic patients.
- People with a history of PAD will demonstrate a continuous decrease of ABI over time, about 0.06 over 4.6 years. On the other side, there is a smaller decrease in the general population it's about 0.025 over 5 years.
- If the ankle pressure is less than 50 mm Hg it is associated with a higher risk of avascularity and amputation.
- Crawford F, Welch K, Andras A, Chappell FM. Ankle brachial index for the diagnosis of lower limb peripheral arterial disease. Cochrane Database of Systematic Reviews. 2016(9).
- Aboyans V, Criqui MH, Abraham P, Allison MA, Creager MA, Diehm C, Fowkes FG, Hiatt WR, Jönsson B, Lacroix P, Marin B. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart Association. Circulation. 2012 Dec 11;126(24):2890-909.
- Xu Y, Xu W, Wang A, Meng H, Wang Y, Liu S, Li R, Lu S, Peng J. Diagnosis and treatment of traumatic vascular injury of limbs in military and emergency medicine: A systematic review. Medicine. 2019 May;98(18).
- St. Michael's Hospital. How to perform an ankle brachial index. Available from: http://www.youtube.com/watch?v=ab_channel[last accessed 18/9/2020]
- McClary KN, Massey P. Ankle Brachial Index (ABI). InStatPearls [Internet] 2020 May 21. StatPearls Publishing.