What Is a Normal Ankle Brachial Index?

Ankle brachial index is a way of checking blood pressure to diagnose peripheral artery disease (PAD).

The ankle-brachial index (ABI) is a procedure done to evaluate a patient for peripheral arterial disease (PAD) in the legs. The ankle-brachial index test is a noninvasive procedure that evaluates the blood flow through the arteries of the legs by checking blood pressure readings. 

Peripheral arterial disease is a type of hardening of the arteries (atherosclerosis) of the legs. The arteries of the legs can become blocked with cholesterol and calcium plaques, decreasing blood flow to the lower legs and feet. PAD is one of the early signs of atherosclerosis in the body and usually precedes heart disease. 

Risk factors for developing peripheral arterial disease include: 

• Age
• Smoking
• High cholesterol
• Obesity
• Poor diet, including red meats and fatty foods
• Sedentary lifestyle
• Diabetes
• Family history of atherosclerosis or heart disease 

The ankle-brachial index is used to evaluate a patient for peripheral arterial disease (PAD) in the legs. It can be used to:

• Diagnose peripheral arterial disease
• As a screening test to assess vascular health in the legs

In the case of trauma or severe injury to the leg, ABI is used to assess the blood flow through the injured tissue to evaluate for severe vascular damage. 

No medications, sedatives, or anesthetic is needed to measure the ankle-brachial index.

• Patients lay on their backs for 10 minutes prior to measurement
• Using a blood pressure cuff (sphygmomanometer), the doctor first measures the blood pressure in both arms, and takes the higher of the two values
• Then, the doctor places the blood pressure cuff on the lower leg, just above the ankle, and measures the blood pressure on both legs. 
• The test lasts 10 to 15 minutes. 

The ankle-brachial index (ABI) is calculated by dividing the ankle pressure by the arm pressure. 

The ankle-brachial index (ABI) measurement ranges are as follows:  

• 0.00-0.40: Severe peripheral arterial disease (PAD) 
• 0.41-0.99: PAD sufficient to cause calf pain with exercise (claudication)
• 1.0-1.40: Normal blood vessels
• Greater than 1.40: Severely calcified blood vessels

Atherosclerotic disease first appears in the legs, so an ABI of 0.90 or less indicates a higher risk of heart disease, stroke, and death. Patients with an ABI of 0.90 or less should be referred for more advanced vascular testing.

An ABI of 0.91-0.99 is considered borderline. Patients with an ABI in this range who have symptoms of pain with exercise should be referred for further vascular testing. 

An ABI of 1.0-1.40 is considered normal. Patients in this range probably do not have peripheral arterial disease. 

In general, there are no risks or complications associated with having an ABI test. It is a non-invasive test that is easy to perform. 

An ankle-brachial index test is not recommended for patients who have known blood clots in the legs.