AIMS:
This test is used as a simple screening test for peripheral vascular disease.
A doctor suspects an obstruction based on the symptoms the patient describes and a pulse that is diminished or absent below a certain point in the leg. Doctors estimate blood flow to a person’s legs in several ways including comparing blood pressure at the ankle with blood pressure in the arm. The ABI compares the blood pressure obtained with the handheld Doppler in the dorsalis pedis or posterior tibial artery (whichever is higher) with the blood pressure in the higher of the 2 brachial pressures.
Additional assessment of waveform at the femoral, popliteal, posterior tibial, anterior tibial and dorsalis pedis may help in the diagnosis of arterial disease.
The ABI has emerged as one of the most potent markers of diffuse atherosclerosis, CV risk and overall survival in various patient populations. An abnormal ABI indicates a threefold CV risk.
PATIENT PREPARATION:
The patient will need to wear a gown (supplied) to easily expose the arms and legs (from the groin to the ankle) for the application of blood pressure cuffs.
TECHNIQUE & TEST DURATION:
The patient is recumbent. The study is non-invasive and painless and does not involve the injection of any dye. The technologist will apply a warm gel to the groin area, ankle (s) and arm (s). A transducer (a small microphone like device) will be placed over various locations on the ankle (s) and leg (s). Additionally, blood pressure readings will be taken of the ankles and the arms. You will not feel any pain however you will feel a mild pressure from the blood pressure cuff and the transducer.
DIAGNOSTIC CRITERIA:
In general, an ABI of >/+0.90 is considered normal, >0.40 to <0.90 reflects mild to moderate peripheral arterial disease and
For a normal ABI in the face of abnormal peripheral arterial circulation (i.e. a false-negative result) in elderly patients or patients with end-stage renal disease or more commonly diabetes mellitus, the ankle arteries indicate the patient may have calcification in the medial layer therefore when the technologist compresses the sphygmomanometer and listens with the Doppler probe the Doppler signal does not disappear at a pressure of >/=250 mmHg. This reading does not translate into a normal ABI but instead indicates vessel calcification and more sophisticated non-invasive tests are required.
NOTE:
Patients with moderate disease of the infrarenal aorta or iliac arteries may have normal arterial circulation at rest but when exercised demonstrate a decrease in ankle pressure. Therefore, a resting study is inadequate for patients with exertional symptoms of intermittent claudication. In this situation, an exercise arterial study should be performed to determine the true etiology of exertional limb pain.
Waveforms may be triphasic, biphasic and monophasic. Monophasic waveforms may indicate a stenosis or occlusion of the artery at the level just proximal to the reading (e.g. monophasic popliteal signal may suggest a superficial femoral artery stenosis or occlusion).
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