View source for Ankle brachial pressure index

The '''Ankle Brachial Pressure Index''' ('''ABPI'''), known more commonly as an ABI, is the ratio of the [[blood pressure]] in the lower legs to the blood pressure in the arms. Compared to the arm, lower blood pressure in the leg is an [[indication]] of blocked arteries ([[peripheral vascular disease]]). The ABI is calculated by dividing the higher [[Systole (medicine)|systolic]] [[blood pressure]] in either the [[dorsalis pedis]] or [[posterior tibial artery|posterior tibial]] arteries by the higher of the two systolic blood pressures in the arms.

==Method==
A [[Medical_ultrasonography#Doppler_sonography|Doppler ultrasound]] blood flow detector, commonly called Doppler Wand or Doppler probe, and a [[sphygmomanometer]] (blood pressure cuff) are usually needed. The blood pressure cuff is inflated [[proximal]] to the artery in question. Measured by the doppler wand, the inflation continues until the pulse in the artery ceases. The blood pressure cuff is then slowly deflated. When the artery's pulse is re-detected through the doppler probe the pressure in the cuff at that moment indicates the systolic pressure of that artery.

The higher systolic reading of the left and right arm [[brachial artery]] is generally used in the assessment. The pressures in each foot's [[posterior tibial artery]] and [[dorsalis pedis artery]] are measured with the higher of the two values used as the ABI for that leg.<ref name="Vowden">{{cite journal |author=Vowden P, Vowden K |title=Doppler assessment and ABPI: Interpretation in the management of leg ulceration |journal=Worldwide Wounds  |month=March |year=2001 |url=http://www.worldwidewounds.com/2001/march/Vowden/Doppler-assessment-and-ABPI.html}} - describes ABPI procedure, interpretation of results, and notes the somewhat arbitrary selection of "ABPI of 0.8 has become the accepted endpoint for high compression therapy, the trigger for referral for a vascular surgical opinion and the defining upper marker for an ulcer of mixed aetiology"</ref>

:<math>ABPI_{Leg} = \frac { P_{Leg} }{ P_{Arm} }</math>
::Where P<sub>Leg</sub> is the systolic blood pressure of dorsalis pedis or posterior tibial arteries
::and P<sub>Arm</sub> is the highest of the left and right arm brachial systolic blood pressure

The ABPI test is a popular tool for the non-invasive assessment of [[Peripheral vascular disease|PVD]].  Studies have shown the [[sensitivity and specificity|sensitivity]] of ABPI is 90% with a corresponding 98% [[sensitivity and specificity|specificity]] for detecting [[hemodynamics|hemodynamically]] significant (Serious) [[stenosis]] >50% in major leg arteries, defined by angiogram.<ref>{{cite journal |author=McDermott MM, Criqui MH, Liu K, Guralnik JM, Greenland P, Martin GJ, Pearce W |title=Lower ankle/brachial index, as calculated by averaging the dorsalis pedis and posterior tibial arterial pressures, and association with leg functioning in peripheral arterial disease |journal=JJ Vasc Surg. |volume=32 |issue=6 |pages=1164–71 |year=2000 |month=December |pmid=11107089 |doi=10.1067/mva.2000.108640 }}</ref>

However, ABPI has known issues:
*ABPI is known to be unreliable on patients with arterial [[calcification]] ([[hardening of the arteries]]) which results in less or incompressible arteries,<ref>{{cite journal |author=Allison MA, Hiatt WR, Hirsch AT, Coll JR, Criqui MH |title=A high ankle-brachial index is associated with increased cardiovascular disease morbidity and lower quality of life |journal=J Am Coll Cardiol.|volume=51 |issue=13 |pages=1292–8 |year=2008 |month=April|pmid=18371562 |doi=10.1016/j.jacc.2007.11.064 }}</ref> as the stiff arteries produce falsely elevated ankle pressure, giving [[false negative]]s<ref>{{cite journal |author=American Diabetes Association|title=Peripheral Arterial Disease in People with Diabetes| journal=Diabetes Care|volume=26|issue=12|pages=3333–3341 | year=2003|month=December|pmid=14633825 |doi=10.2337/diacare.26.12.3333 }}</ref>). This is often found in patients with [[diabetes melitus]]<ref>{{cite journal |author=Aboyans V, Ho E, Denenberg JO, Ho LA, Natarajan L, Criqui MH |title=The association between elevated ankle systolic pressures and peripheral occlusive arterial disease in diabetic and nondiabetic subjects | journal=J Vasc Surg.|volume=48|issue=5|pages=1197–203 |year=2008 |month=November|pmid=18692981 |doi=10.1016/j.jvs.2008.06.005 }}</ref> (41% of PAD patients have diabetes<ref>{{cite journal |author=Novo S|title=Classification, epidemiology, risk factors, and natural history of peripheral arterial disease| journal=Diabetes Obes Metab.|volume=4|supplement=2|pages=S1–6 |year=2002|month=March|pmid=12180352 |doi=10.1046/j.1463-1326.2002.0040s20s1.x }}</ref>), [[renal failure]] or heavy [[tobacco smoking|smoker]]s. ABPI values < 0.9 & >1.3 should be investigated further regardless.
*Performing ABPI is time consuming.<ref>{{cite journal |author=Doubeni CA, Yood RA, Emani S, Gurwitz JH|title=Identifying unrecognized peripheral arterial disease among asymptomatic patients in the primary care setting| journal=Angiology|volume=57|issue=2|pages=171–80 |year=2006|month=March-April|pmid=16518524 |doi=10.1177/000331970605700206 }}</ref>
*Resting ABPI is insensitive to mild PAD.<ref>{{cite journal |author=Stein R, Hriljac I, [[Jonathan L. Halperin | Halperin JL]], Gustavson SM, Teodorescu V, Olin JW |title=Limitation of the resting ankle-brachial index in symptomatic patients with peripheral arterial disease | journal=J Vasc Med.|volume=11|issue=1|pages=29–33 |year=2006|month=February|pmid=16669410 |doi=10.1191/1358863x06vm663oa }}</ref> Treadmill tests (6 minute) are sometimes used to increase ABPI sensitivity,<ref>{{cite journal |author=Montgomery PS, Gardner AW,|title=The clinical utility of a six-minute walk test in peripheral arterial occlusive disease patients | journal=J Am Geriatr Soc. |volume=46|issue=6|pages=706–11|year=1998|month=June|pmid=9625185 }}</ref> but this is unsuitable for patients who are obese or have co-morbidities such as [[Aortic aneurysm]], and increases assessment duration.
*Lack of protocol standardisation,<ref>{{cite journal |author=Jeelani NU, Braithwaite BD, Tomlin C, MacSweeney ST|title=Variation of method for measurement of brachial artery pressure significantly affects ankle-brachial pressure index values| journal=Eur J Vasc Endovasc Surg.|volume=20|issue=1|pages=25–8|year=2000|month=July|pmid=10906293 |doi=10.1053/ejvs.2000.1141 }}</ref> which reduces intra-observer reliability.<ref>{{cite journal |author=Caruana MF, Bradbury AW, Adam DJ|title=The validity, reliability, reproducibility and extended utility of ankle to brachial pressure index in current vascular surgical practice| journal=Eur J Vasc Endovasc Surg.|volume=29|issue=5|pages=443–51|year=2005|month=May|pmid=15966081 |doi=10.1016/j.ejvs.2005.01.015}}</ref>
*Skilled Operators are required for consistent, [[accurate]] results.<ref>{{cite journal |author=Kaiser V, Kester AD, Stoffers HE, Kitslaar PJ, Knottnerus JA|title=The influence of experience on the reproducibility of the ankle-brachial systolic pressure ratio in peripheral arterial occlusive disease| journal=Eur J Vasc Endovasc Surg.|volume=18|issue=1|pages=25–9|year=1999|month=July|pmid=10388635 |doi=10.1053/ejvs.1999.0843 }}</ref>


However, technology is emerging that allows for the oscillometric calculation of ABI. This is achieved by doing simultaneous readings of blood pressure at the levels of the ankle and upper arm using specially calibrated oscillometric modules. This idea has been pioneered by Uwe DIEGEL and Roland ASMAR in France. The main interest in the introduction of an oscillometric system to measure ABI is that it standardizes the method and makes the measurement of ABI accessible to all doctors.

==Interpretation of results==
In a normal subject the pressure at the ankle is slightly higher than at the elbow (there is reflection of the pulse pressure from the vascular bed of the feet, whereas at the elbow the artery continues on some distance to the wrist).  The ABPI is the ratio of the highest ankle to brachial artery pressure and an ABPI of greater than 0.9 is considered normal (Free from significant [[Peripheral artery occlusive disease|PAD]]). 

However, an ABPI value greater than 1.3 is considered abnormal, and suggests [[calcification]] of the walls of the arteries and incompressible vessels, reflecting severe [[peripheral vascular disease]].

Provided that there are no other significant conditions affecting the arteries of the leg, the following ABPI ratios can be used to predict the severity of PAD as well as assess the nature and best management of various types of leg [[Skin ulcer|ulcers]]:<ref name="Vowden" />
{| class="wikitable"
!ABPI value || Interpretation || Action || Nature of [[Ulcer (dermatology)|ulcers]], if present 
|-
| above 1.2 || Abnormal<br/>Vessel hardening from PVD || Refer routinely || rowspan="4" | [[Venous ulcer]]<br/>use full [[Bandage#Compression bandage|compression bandaging]]
|-
| 1.0 - 1.2 || Normal range || rowspan="2" | None
|-
| 0.9 - 1.0 || Acceptable
|-
| 0.8 - 0.9 || Some arterial disease || Manage risk factors
|-
| 0.5 - 0.8 || Moderate arterial disease || Routine specialist referral || Mixed ulcers<br/>use reduced compression bandaging. [[Claudication]] may be present at values less than 0.6.<ref name="isbn0-7817-2771-5">{{cite book |author=Sawyer, Robert J.; Traves D. Crabtree; Eugene F. Foley |title=Surgical specialties |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2000 |pages=3 |isbn=0-7817-2771-5 |oclc= |doi= |accessdate=}}</ref>
|-
| under 0.5 || Severe arterial disease  || Urgent specialist referral || Arterial ulcers<br/>no compression bandaging used. Pain at rest may be present at values less than 0.25.<ref name="isbn0-7817-2771-5">{{cite book |author=Sawyer, Robert J.; Traves D. Crabtree; Eugene F. Foley |title=Surgical specialties |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2000 |pages=3 |isbn=0-7817-2771-5 |oclc= |doi= |accessdate=}}</ref>
|}

==Predictor of atherosclerosis mortality==
Studies in 2006 suggests that an abnormal ABPI may be an independent predictor of mortality, as it reflects the burden of [[atherosclerosis]].<ref name="pmid16534039">{{cite journal |author=Feringa HH, Bax JJ, van Waning VH, ''et al.'' |title=The long-term prognostic value of the resting and postexercise ankle-brachial index |journal=Arch. Intern. Med. |volume=166 |issue=5 |pages=529–35 |year=2006 |month=March |pmid=16534039 |doi=10.1001/archinte.166.5.529 |url=}}</ref><ref name="pmid16505519">{{cite journal |author=Wild SH, Byrne CD, Smith FB, Lee AJ, Fowkes FG |title=Low ankle-brachial pressure index predicts increased risk of cardiovascular disease independent of the metabolic syndrome and conventional cardiovascular risk factors in the Edinburgh Artery Study |journal=Diabetes Care |volume=29 |issue=3 |pages=637–42 |year=2006 |month=March |pmid=16505519 |doi= 10.2337/diacare.29.03.06.dc05-1637|url=http://care.diabetesjournals.org/cgi/content/full/29/3/637}}</ref>

==See also==
*[[Peripheral vascular disease]]
*[[Peripheral vascular examination]]
*[[Intermittent claudication]]

==References==
{{reflist|2}}

{{Physical exam}}
{{Vascular procedures}}
[[Category:Cardiovascular system]]
[[Category:Medical tests]]
[[Category:Medical ultrasound]]

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