Ankle brachial pressure index (ABPI)
The ABPI is the ratio of the ankle systolic blood pressure to the brachial systolic blood pressure. ABPI is measured using a sphygmomanometer and handheld Doppler device. ABPI measurement is available in specialised wound clinics, community nursing services, podiatry services, some primary care settings and vascular practices. A video showing how to undertake an ABPI is available here.
An ABPI less than 0.9 indicates peripheral arterial disease. An ABPI between 0.9 and 1.3 is considered normal (ie the patient does not have peripheral arterial disease). Although the APBI is a useful noninvasive diagnostic test for objective assessment of arterial disease, it cannot be used for patients with calcified vessels (eg in patients with diabetes, kidney disease, age over 75 years). Calcified arteries are noncompressible, causing an artificially inflated arterial systolic blood pressure and subsequently elevating the ABPI. For patients with an ABPI above 1.3, or if the ABPI result does not fit within the clinical context of the patient, a toe pressure or toe brachial pressure index may be useful; see Assessment for peripheral arterial disease. An arterial duplex scan may be useful when clinical assessment suggests arterial impairment, and referral to a vascular specialist may be necessary; see Arterial leg ulcers.
The APBI guides compression therapy for venous leg ulcers. ABPI values used for compression therapy are different to those used to diagnose peripheral arterial disease. International expert consensus on correlating the ABPI to levels of compression for venous leg ulcers is lacking. However, general rules for selecting compression therapy based on the ABPI are1:
- for any ABPI, if pedal pulses are not palpable—do not apply compression and seek expert advice
- ABPI 0.5 or less—compression is contraindicated (see Overview of assessment and management of arterial leg ulcers)
- ABPI above 0.5 up to 0.8—use class II compression with frequent monitoring, or class I if frequent monitoring is not possible
- ABPI above 0.8 up to 1.3—use class III compression, or lower if not tolerated
- ABPI above 1.3—further assessment is required; seek specialist advice.
Repeat ABPI regularly (eg 6 monthly) as part of a thorough clinical review in patients with nonhealing ulcers to exclude progression of arterial disease.