ABI — ankle-brachial index

Interactive tool

Calculate the left and right ABI

Enter the systolic pressures measured with a continuous Doppler probe (8–10 MHz) and an appropriate cuff. Fields left empty are ignored: to calculate just one side, the highest brachial pressure and the pressures of that ankle are sufficient.

Come si usa

Instructions for use

Patient preparation

1. Patient in decubito supino da almeno 5–10 minuti, in ambiente termicamente confortevole, testa e talloni appoggiati.
2. No smoking, coffee or exercise in the previous 30 minutes.
3. Bracciale di larghezza pari ad almeno il 40% della circonferenza dell'arto; su caviglie molto edematose usare un bracciale più largo.
4. CW Doppler probe 8–10 MHz with an angle of 45–60° with respect to the vessel axis, abundant gel.

Measurement sequence

1. Brachiale destra → tibiale posteriore destra → pedidia destra → pedidia sinistra → tibiale posteriore sinistra → brachiale sinistra. La sequenza a “U” riduce l'effetto dell'ansia da primo rilievo.
2. Inflate 20 mmHg beyond the disappearance of the signal, deflate at 2 mmHg/s and record the pressure at ricomparsa del segnale Doppler (non ai toni di Korotkoff).
3. If the two brachials differ by more than 15–20 mmHg, repeat both: a confirmed difference suggests subclavian stenosis and should be reported in the report.

Compiling the calculator

• Enter entrambe le pressioni brachiali: the denominator is always the higher of the two, for both lower limbs.
• For each ankle insert tibialis posterior and pedis: the numerator is la più alta delle due (AHA/ESC recommended method for diagnosing PAD).
• If an artery cannot be found, leave the field blank and note it in the report: the calculation uses the other one.
• The result also reports the differenza interbrachiale and reports values ​​above 1.40 (incompressible arteries), which make the ABI uninterpretable and require the transition to TBI.

Riferimenti clinici

Guidelines and interpretation

The thresholds below follow the ESC/ESVS recommendations on peripheral arterial disease and the AHA scientific statement on the measurement and interpretation of ABI, implemented by the Global Vascular Guideline on chronic limb-threatening ischemia.

ABI as a cardiovascular risk marker

An ABI ≤ 0.90 approximately doubles mortality cardiovascular at 10 years at parity of traditional risk score, and the same goes for values ​​> 1.40: the relationship with risk is “U” shaped. This is what the ABI is for recommended as a reclassification test in subjects at intermediate risk and as screening in long-term diabetics, smokers and those over seventy.

Rapporto con l'ecocolordoppler

• L'ABI quantifica il danno emodinamico complessivo dell'arto, l'ecocolordoppler ne localizza the cause: the two tests are complementary and must be reported together in the report.
• A normal ABI at rest does not exclude a well-compensated isolated iliac stenosis: if clinical suspicion is high, post-exercise ABI and direct study of the iliac axis are needed.
• In the follow-up of a bypass or angioplasty, a fall in the ABI ≥ 0.15 compared to the previous control is the alarm criterion for restenosis, regardless of the absolute value.
• In the diabetic foot the ABI is frequently falsely normal or elevated: the staging of ischemia in the classification WIfI favors digital pressure and TCP₂.

Bibliografia

Sources

• ESC/ESVS 2024 — Guidelines for the management of peripheral arterial and aortic diseases, European Heart Journal.
• AHA Scientific Statement (Aboyans V. et al., Circulation 2012) — Measurement and interpretation of the ankle-brachial index.
• Global Vascular Guidelines (Conte MS. et al., J Vasc Surg 2019) — Management of chronic limb-threatening ischemia.
• ABI Collaboration (JAMA 2008) — Ankle brachial index combined with Framingham risk score to predict cardiovascular events and mortality.