General Review

Measurement, Calculation, and NormalRange of the Ankle-Arm Index: ABibliometric Analysis and Recommendationfor Standardization

Steven Klein, MD, and J. Joris Hage, MD, PhD, Amsterdam, The Netherlands

Since its introduction in 1950, a variety of methods of measurement and calculation have beenused to establish the ankle-arm index (AAI). This has resulted in variations of its normal rangeand difficulty in comparing study results. Hence, the objective of our study was to analyze thedisparate methods used to assess AAI and its normal range and to recommend a standardizedmethod to assess AAI based on that analysis. We made an inventory of the disparate AAImethods and its normal range reported in 100 randomly selected publications and recommendthe means of such standardization. We recommend that an experienced observer assess AAIwith the patient at rest in the supine position. The width of the sphygmometer cuffs should be 1.5times that of the extremity to be measured, and brachial and crural pulses should be detectedusing a Doppler device. Systolic pressures should be measured at both arms and over theanterior and posterior arteries of both legs, with the cuff placed just proximally to the malleoli.The left arm pressure ought to be used as denominator and the mean of pressures of both cruralarteries of each leg ought to be used for the numerator of the AAI for that leg. We advocate 0.90as the cut-off value to distinguish patients who need further arterial assessment.

INTRODUCTION

The ankle-arm index (AAI) is the ratio of systolic

blood pressure at the level of the ankle to that at

the level of the arm.1 Because this noninvasive

method is simple, reproducible,2-6 and accurate at

detecting the decreased blood pressure distal to an

arterial stenosis,7-9 it is often used to assess

peripheral arterial occlusive disease (PAOD). Since

the introduction of the concept of the AAI by

Winsor, in 195010 and its popularization by Yao

et al. in 1969,11 a wide variety of methods of AAI

measurement and calculation have been used in

studies on its diagnostic and epidemiological value.

Use of these nonuniform and nonstandardized

methods has resulted in variations of reportedly

‘‘normal’’ versus ‘‘abnormal’’ distribution of AAI.

This results in confusion and hampers adequate

comparison of results from one study to another.

Moreover, it prohibits the development of an evi-

dence-based diagnostic approach. Therefore, the

objective of our study was to make an analysis of

the disparate methods used to assess AAI and its

normal range and to recommend a standardized

method to assess AAI based on that analysis.

MATERIALS AND METHODS

Selection of 100 Publications on AAI

Our method of bibliometric analysis has been pre-

viously tried and described.12 Briefly, it seeks to

Section of Surgical Disciplines, Antoni van Leeuwenhoek Hospital,Amsterdam, The Netherlands.

Correspondence to: J. Joris Hage, MD, PhD, Section of SurgicalDisciplines, Antoni van Leeuwenhoek Hospital, Plesmanlaan 121, NL-1066 CX, Amsterdam, The Netherlands, E-mail: j.jorishage@inter.nl.net

Ann Vasc Surg 2006; 20: 282-292DOI: 10.1007/s10016-006-9019-x� Annals of Vascular Surgery Inc.Published online: March 23, 2006

282

reproducibly trace and analyze publications on a

certain topic, in this case the methodology of AAI

assessment. To do so, we considered all original

studies and reviews indexed in Pubmed or the

medical library of the University of Amsterdam,

The Netherlands, that featured the term ankle-arm

index or ankle-brachial index in the abstract for

inclusion in our analysis. Using the Pubmed search

engine (http://www.ncbi.nlm.nih.gov/ accessed

November 18, 2004) and the search engine of the

medical library, 812 medical journal articles and 32

book chapters were traced. As our purpose was to

review the variation of techniques of AAI assess-

ment rather than to calculate quantitative esti-

mates of the outcome of these assessments, we

used simple random sampling to select 100 publi-

cations that mentioned use of AAI as the method to

distinguish PAOD.13 Doing so, we came across 13

publications that neither mentioned what methods

had been used to assess and calculate the AAI nor

referred to any other report to provide any indi-

cation as to what method was used. Hence, these

13 publications were excluded, and instead, 13

other publications were randomly selected.

Assessment of Data from the Publications

The 100 publications were systematically analyzed

for indications as to what method of AAI assessment

had been used by the author(s). As such, we scored

on 11 key points of measurement and calculation.

Apart from data provided in each publication on (1)

the position of the patient during measurement, we

noted information on (2) the width of the cuff of the

sphygmometer used for the arm, (3) the width of

the cuff of the sphygmometer used for the lower leg,

(4) the level of placement of this cuff on the lower

leg, (5) the method of detection of the pulse in the

arm, (6) the method of detection of crural pulses,

(7) whether or not the brachial pressure was mea-

sured bilaterally, (8) whether or not crural pres-

sures were measured bilaterally, (9) which of the

crural pulses were assessed to calculate the AAI

(anterior tibial, posterior tibial, or peroneal), (10)

which of the brachial and crural pressures were

used for the AAI denominator and numerator, and

(11) the cut-off value for the normal AAI. To not

further complicate the grouping of various ranges of

distribution of normal AAI, no difference was made

between ‘‘lower than ()’’ and ‘‘equal to or lower

than ( £ )’’ or between ‘‘higher than (>)’’ and

‘‘equal to or higher than (‡).’’ Likewise, no atten-

tion was paid to the mean and range indicated for

the different stages of PAOD because we did not

intend to describe these stages.

Whenever the methodology of any of the 11

scored items was not indicated in the text of the

publication, the references provided by the au-

thor(s) were searched for such an indication. Still,

when authors described the methods they had used

and referred to other studies to motivate their

choice of method, we did not check whether the

described method corresponded with the reported

source method.

RESULTS

Information on Patient Position during

Assessment of AAI

In 60 of the 100 analyzed reports, the supine po-

sition was mentioned as the position used to mea-

sure the brachial and crural blood pressures. Only a

reference to other studies indicated the position in

nine of the other 40 reports. Still, two of these nine

references failed to mention this position. The

remaining 31 reports offered neither information

on the position of the patient nor a reference to

indicate this position.

Information on Sphygmometer Cuff Width

Used to Assess Brachial Blood Pressure

While describing the method of AAI measurement,

a single largest group of 56 (groups of) authors did

not provide any information as to the size of the cuff

that was used to assess the brachial blood pressure.

Twenty-one (groups of) authors stipulated what

size of cuff was used, and of these, nine used a cuff

of 12 cm,3,4,14-20 two a cuff of 13 cm,21,22 two a cuff

of 14 cm,23,24 and three a cuff of 15 cm.25-27 One

author measured the circumference of the arm to

determine the proper cuff width,28 and a cuff of 1.5

times the diameter of the arm was used in two

studies.7,29 One group of authors used either a 14

or a 17 cm cuff, depending on the size of the pa-

tient�s arm. The one remaining of these 21 (groups

of) authors reported using a pediatric cuff (8 cm) to

assess AAI in children.30

In 10 studies, the cuff size was reported to have

been ‘‘appropriate’’ or ‘‘carefully selected’’,31-40

whereas a ‘‘standard’’ cuff was reportedly used in

five.41-45 Eight (groups of) authors9,21,46-52 referred

to other studies for their method of AAI assess-

ment, but in seven of these references, no infor-

mation on cuff size was provided either.

Information on Sphygmometer Cuff Width

Used to Assess Crural Blood Pressure

A majority of 52 (groups of) authors did not pro-

vide any information as to the size of the cuff used

Vol. 20, No. 2, 2006 Ankle-arm index revisited 283

to take the crural blood pressure while describing

the method of AAI measurement.

Twenty-six (groups of) authors stipulated what

size of cuff was used. Of these, one used a cuff of 10

cm,53 11 a cuff of 12 cm,1,3,4,15-20,38,54 two a cuff of

12.5 cm,55,56 two a cuff of 13 cm,21,22 one a cuff of

13.5 cm, 5 two a cuff of 14 cm,23,24 and three a cuff

of 15 cm.25-27 Three (groups of) authors used a cuff

of 1.2 or 1.5 times the diameter of the leg,7,29,57 and

again, the one remaining of these 26 (groups of)

authors reported using a pediatric cuff of 8 cm

width to assess AAI in children.30

In nine studies, an ‘‘appropriate’’ or ‘‘carefully

selected’’ sized cuff was used,31-37,39,40 whereas use

of a ‘‘standard’’ cuff was reported in three.41,43,44

An arm-cuff size was probably used at the ankle in

two of the studies.42,45

Finally, eight (groups of) authors referred to

other studies for their method of AAI assess-

ment,9,21,46-52 but again, no information on cuff

size was provided in seven of these references.

Information on Sphygmometer Cuff Position

on the Lower Leg

In 54 studies, the cuff position on the lower leg was

indicated by either ‘‘ankle (or malleolus)’’ (n = 24),

‘‘proximal to malleoli (or ankle)’’ (n = 27), ‘‘as

distal as possible on the calf’’ (n = 1), ‘‘lower 1/3 of

lower leg’’ (n = 1), or the ‘‘posterotibial level’’

(n = 1).

Eight (groups of) authors referred solely to other

studies for their method of AAI assessment, but in

two of these, no information on the position of the

crural cuff was provided in the reference either.

Thirty-eight studies provided no indication as to

the position of the crural cuff, while other aspects

of the AAI assessment were described.

Information on the Method of Detection of

the Pulse in the Arm

In 58 of the 100 studies, the brachial pulse was

detected with a pencil-Doppler device, whereas

auscultation was used for this in six.11,15,18,55,57,58

Other techniques used were the Dynamap

(n = 7)15,25,26,32,53,59,60 and photoplethysmography

(n = 2).10,35 The technique of assessment of the

arm systolic pressure was not mentioned in 23 re-

ports. In seven reports,46-52 reference was made to

other studies to indicate the method of assessment,

but these references were not always clear on the

method used either.

The number of techniques totaled 103 rather

than 100 because Jeelani et al.15 used Dynamap

and auscultatory methods in addition to the pencil-

Doppler to compare these three methods of pulse

detection and Yao et al.11 used both the ausculta-

tory method and the pencil-Doppler.

Information on the Method of Detection of

the Pulse in the Leg

A vast majority of 77 (groups of) authors reported

using a pencil-Doppler to detect the crural pulses.

Of these, Strandness and Sumner7 used capacitance

pulse pick-ups and plethysmography in addition to

the pencil-Doppler, whereas Carter55 also used

capacitance pulse pick-ups, visual flush technique,

and spectroscopy. They did so to compare the

influence of these methods on AAI measurements.

One author used solely capacitance pulse pick-

ups for pulse detection,56 whereas three authors

used solely plethysmography.10,18,61 Other meth-

ods used to detect the crural pulses were the Dy-

namap (n = 5) 25,26,32,59,62 and the strain-gauge

technique (n = 4).21,57,63,64

Seven (groups of) authors (7%) referred to other

studies to indicate their method of assessment of

crural pulses.46-52 However, three of those seven

(groups of) authors referred to more than one other

study and, because different techniques were used

in these references, it remained unclear which

technique they had actually used. Finally, three of

the 100 studies did not report at all what kind of

device was used for crural pulse detection.65-67

Information on Whether or Not Brachial

Pressure Was Measured Bilaterally

A single largest group of 47 (groups of) authors

measured the brachial blood pressure at both

arms to determine the denominator of the AAI

formula. Fourteen other reports stipulated the

blood pressure to be measured at the right

arm,2,6,23,38,42,54,58,60,61,68-72 whereas one other

indicated the left arm to be used.19 According to

five reports, the blood pressure may be taken on

either arm.9,10,29,32,73

Twenty-six (groups of) authors did not specify

which arm was used, and seven (groups of) authors

only provided a reference for the method they had

used.46-52

Information on Whether or Not Crural

Pressures Were Measured Bilaterally

A vast majority of 96 (groups of) authors measured

the crural blood pressure at both legs to separately

distinguish the presence of PAOD in each leg. Of

these, eight (groups of) authors36,37,53,54,60,61,72,74

reported measuring both legs and using the lowest

284 Klein and Hage Annals of Vascular Surgery

of the bilateral blood pressures to determine the

presence of PAOD in their patients. Shinozaki et

al.23 and Zheng et al.32 reported diagnosing PAOD

by measuring the AAI of just one leg. Two authors

did not provide any information about whether

one or two legs were measured.75,76

Information on Which Crural Pulses Were

Assessed for AAI

In 33 studies, both the pressures over the posterior

tibial artery (PT) and the dorsal pedal or anterior

tibial artery (DP/AT) were measured before calcu-

lating AAI (Table I). The peroneal artery (PA) pulse

was assessed in addition to that of the PT and DP/

AT in three studies. Twenty-three studies recom-

mended using the pressures over the PT or DP/AT

for the numerator of the AAI. Three of these 23

advocated use of the best audible flow signal.3,41,69

In 13 studies, the crural pulse was detected only at

the PT.

No specification of the crural artery other than

‘‘ankle’’ was provided to indicate which of the

crural or pedal pulses were detected in 18 reports.

In 10 of these 18 reports, this remained unclear

because of the method used for crural pulse

detection (strain-gauge, plethysmography, capaci-

tance pulse pick-up, spectroscopy, visual flush

technique, or Dynamap).10,18,21,25,26,56,57,61,63,64

Three reports did not clarify which pedal artery

was used to detect the crural pressure, whereas

seven (groups of) authors referred to other studies

for their method of AAI assessment. Two of these

seven references merely mentioned ‘‘ankle’’ as the

location of pulse detection.

Information on Which of the Brachial and

Crural Pressures (Highest, Mean, Median, or

Lowest) Were Used for Denominator and

Numerator of AAI

No fewer than 39 different ways to calculate AAI

were reported in 77 of the 100 studies. Among

these, the formulas provided most often were as

follows: AAI = highest of PT and DP/AT pressures/

highest arm pressure (n = 15), AAI = ankle pres-

sure/arm pressure (n = 9), and AAI = PT or DP/AT

pressure/arm pressure (n = 8). Seven times we

found the same (group of) author(s) to have used

two different formulas in two different stud-

ies.19,25,26,28,37,55,56,60,72,77-81 Confusing matters

even further, some authors used more than one

formula in a single study.28,31,36,55

The remaining 23 (groups of) authors did not

report the formula they had used to calculate the

AAI. Eight of these 23 provided a reference for the

formula, whereas 15 did not.

Of the 47 (groups of) authors who measured

systolic pressure at both arms, the highest pressure

found was used for the denominator of the AAI in

38 studies, whereas the mean of both arm pressures

was used in 11 studies. This totals 49 rather than 47

studies because Hiatt et al. twice compared two

different ways of calculating the denominator.28,78

The lowest pressure of both arms was never re-

ported to have been used as denominator.

Seven (groups of) authors used both the PT and

the DP/AT for the numerator of separate

AAIs.2,14,20,33,34,78,82

Twenty-nine more (groups of) authors used

more than one detected pressure for the definite

calculation of the numerator. In 23 of these 29

studies, the highest of the two or three crural blood

pressures was used for the numerator, whereas the

lower was used in the five and the mean of those

pressures in four. Again, this totals 32 rather than

29 studies because Hiatt et al.28 compared two

methods (average and lower) while McGrae

McDermott et al.31 compared three methods

(average, higher, and lower) to calculate the

numerator of the AAI.

Cut-off Value of the Normal AAI

Some (groups of) authors defined a lower limit of

AAI for the absence of PAOD, whereas others

provided an upper limit felt to be indicative of the

Table I. The 100 publications that were studied divided according to the information provided on the

crural pulses used to assess AAI numerator

Description Number of reports

PT and DP/AT n = 332,4,14,16,17,20,28,31,33-35,37,39,40,46,53-55,62,65,74-76,78,82,93-100

PT, DP/AT, and PA n = 327,101,102

PT or DP/AT n = 233,7,19,24,29,30,36,41,43,56,66,67,69,73,77,79,81,90,103-107

PT only n = 131,6,22,23,32,38,58-60,71,72,85,108

‘‘Ankle’’ n = 185,10,11,18,21,25,26,42,44,45,57,61,63,64,68,70,80,109

No information n = 315,84,110

References for method n = 79,47-52

Vol. 20, No. 2, 2006 Ankle-arm index revisited 285

presence of PAOD. Still others considered these two

cut-off values to be the same, thus defining one

AAI below which PAOD was accepted to be present

and above which it was not.

The lower cut-off value of a normal AAI as of-

fered in 58 of the 100 studies varied from 0.85 to

1.10, but most often, 1.00 was cited for this (Ta-

ble II).

Eight different upper AAI limits indicative of

PAOD were cited in 60 of the 100 studies. Although

these varied from 0.80 to 1.00 (Table III), 0.90 was

most often used as this cut-off value.

Rather than one cut-off value, Lennihan and

MacKereth44 cited median AAI values for subjects

with and without claudication. Eighteen reports

mentioned the method of assessment but lacked

any information on its normal or abnormal limits.

Three additional (groups of) authors provided ref-

erences for information on these limits.47,48,50

Neither a description nor a reference was found in

one study.83

COMMENTS AND RECOMMENDATIONS

Although AAI assessment currently is the most

common diagnostic instrument for the detection

and quantification of PAOD,33,77,84 the repeatabil-

ity of assessment continues to be subject to con-

troversy.2,33,77,83,85,86 The variability of AAI

assessment attributable to observers, timing of

measurement, and repeated measures is consider-

ably less than that attributable to biological factors.

Estimates of intraobserver variability range from

7.3% for experienced observers to 12% for less-

experienced observers,5,6,19,87 and repeated

measurements may decrease this variability.2,19

Standardized, repeated measurement of AAI by

experienced observers is sufficiently accurate to

guide clinical decision making.77,87 When the art

and science of AAI measurement and calculation

are being taught or discussed, moreover, it is

important that all involved are speaking of the

same standard. Even when limited to 100 publi-

cations, however, our bibliometric analysis yielded

a great variety of methodology. This indicates that

there is still need for a consensus on the method of

AAI measurement.

Before we present our recommendations to

come to such consensus, some potential limitations

of our study need to be addressed. As such, we

stress that ours are not evidence-based suggestions.

Because of the variety of methodology, any and all

of such suggestions would lack an adequate level of

evidence. Furthermore, we did not score for po-

tential key points such as minimum resting time

prior to measurement, room temperature, or fre-

quency of Doppler probe since these were rarely

mentioned in the 100 reviewed publications.

Hence, ours are merely recommendations provided

in an attempt at the standardization that is urgently

needed to allow comparison and meta-analysis of

future study results.

Position of the Patient during Measurement

The supine position seems to be the position of

choice to assess AAI because the influence of height

of the subject and his or her blood column pressure

on AAI may be prevented only in this position. Less

agreement exists on the routine use of premea-

surement exercise. Such exercise may be needed

since the ankle pressure may be normal at rest in

patients with mild PAOD and there may be ade-

quate collateral flow around the arterial occlu-

sions.8 Even though such PAOD may only be

detectable after exercise, exercise influences the

heart rate during measurement, which in turn

influences AAI.25 Hence, in studies where AAI is

measured during exercise, this should be men-

tioned in the Methods section.

Width and Level of the Sphygmometer

Cuff(s)

If the width of the sphygmometer cuff is too nar-

row in comparison to the extremity (‘‘undercuff-

Table II. Reports categorized according to information provided on the lower limits of the range of AAI in

subjects without PAOD

Cut-off value Number of reports

AAI = 0.85 n = 174

AAI = 0.90 n = 1720,31,32,34,36,40,45,46,53,60,67-9,71,77,97,98

AAI = 0.92 n = 1102

AAI = 0.95 n = 61,81,82,84,103,104

AAI = 0.97 n = 34,9,55

AAI = 1.00 n = 287,10,11,16,18,19,21-23,29,38,39,41,42,54,56,66,70,72,73,75,80,99-101,105,106,108

AAI = 1.10 n = 259,80

286 Klein and Hage Annals of Vascular Surgery

ing’’), the blood pressure reading will be errone-

ously high, whereas the reading may be too low if

the cuff is too wide (‘‘overcuffing’’).88 Ideally, the

cuff width should be at least 1.5 times the diameter

of that part of the extremity where the pressure is

being measured,7 and the size of the cuff should be

adjusted in obese patients or in patients with odd-

shaped arms or ankles.88 Still, calcification in the

arterial wall can result in spuriously high readings

of the systolic pressure,7,29 and this may not be

corrected by the use of a wider cuff.

As to the position of the cuffs at the extremities,

general agreement exists on placement just proxi-

mal to the elbow on the upper arm and just prox-

imal to the malleoli at the lower leg.

Method of Detection of the Pulse in the Arm

and Leg

From their comparison of three methods of mea-

surement of brachial systolic blood pressure, Jee-

lani et al.15 concluded that the technique of

measurement significantly affects the calculation of

AAI. As they found a 20% margin of error, these

authors advocated the use of just one technique to

limit inter- and intraobserver errors. For this, use of

a pencil-Doppler should be considered the method

of choice to detect the brachial pulse as this was

already done in half of the reviewed studies.

Measurements by Doppler device were proven at

high, medium, and low blood pressures to correlate

with systolic pressure measurement obtained by

conventional methods.10,11

Carter55,56 observed good agreement between the

values of systolic blood pressure obtained by four

different methods of monitoring the crural pulses

(pulse pick-ups, pencil-Doppler flow detection,

spectroscopy, and visual flush), and capacitance

pulse pick-up even allows for detection of nonpal-

pable pulses.7 Still, allegedly normal crural blood

pressures can be recorded with pulse pick-up, spec-

troscopic, and visual flush methods as long as only

one crural artery is patent, whereas the pencil-

Doppler may provide information on individual

tibial vessels.55,56 Pencil-Doppler readings are highly

correlated to intra-arterial pressure readings.7,89

Moreover, ultrasonography is less cumbersome than

plethysmography and more reliable than the aus-

cultation method, which has a 10% failure rate in

obtaining ankle pressures in normal individuals.90

Although the accuracy of measurement with the

Dynamap may be higher than that with pencil-

Doppler, the Dynamap is not available everywhere.

For this reason, we recommend the pencil-Doppler

device as the standard instrument to measure both

the brachial and crural blood pressures.

Whether or Not to Bilaterally Measure theBrachial Pressure and Which One to Use for

Denominator

A majority of authors measured the systolic pres-

sures of both arms to assess the denominator of the

AAI. A minority measured only one arm, and of

these, only one indicated using the left arm.19 This

is remarkable as the blood pressure used for the

denominator of the AAI should be measured at the

left arm in cases where aortic coarctation results in

a difference of blood pressure in the right and left

arms.28,31,36 In these cases, a difference of 5-10 mm

Hg warrants further examination, while a differ-

ence of 20 mm Hg between the arms indicates se-

vere stenosis.91 In general, AAI calculated on the

basis of systolic pressure at the left arm was 0.02

lower than that at the right arm.78 For these rea-

sons, we advise taking the blood pressure at both

arms to rule out serious differences and using that

of the left arm to calculate the AAI denominator.

Whether or not to Bilaterally Measure Crural

Pressures and Which of These to Use as

Numerator

In the healthy population, the differences between

the systolic pressures of the DP/AT and PT do not

Table III. Reports categorized according to information provided on the upper limits of the range of AAI in

subjects with PAOD

Description Number of reports

AAI = 0.80 n = 821,33,52,54,63,70,80,96

AAI = 0.85 n = 224,74

AAI = 0.90 n = 319,18-20,31-34,36-38,40,45,46,51,53,57,60,64,67-69,71,72,76,77,80,85,97,98,107

AAI = 0.92 n = 239,49

AAI = 0.94 n = 128

AAI = 0.95 n = 481,84,103,104

AAI = 0.97 n = 23,4

AAI = 1.00 n = 1010,11,16,22,23,66,101,106,108,109

Vol. 20, No. 2, 2006 Ankle-arm index revisited 287

exceed 10 mm Hg.55 In general, the AAI at the DP/

AT was found to be 0.04 lower than that at the

PT.78 PAOD may, however, separately affect each

of the main arteries, and a difference of over 15

mm Hg between the DP/AT and the PT may pro-

vide a useful clue about the involvement of the

individual crural arteries by the occlusive pro-

cess.8,55

Difference in pressure readings between the DP/

AT and PT in the same limb, as well as an abnormal

AAI of both the DP/AT and PT in the same leg,

should be considered indicative of PAOD.8,55 Be-

cause PAOD may also affect both legs separately,

moreover, we advise bilaterally measuring the

blood pressure of both the DP/AT and the PT.

How to Calculate the AAI Numerator and

Denominator

Numerator. McGrae McDermott et al.31 per-

formed a multiple linear analysis to identify which

one out of three commonly used formulas to cal-

culate the AAI was most closely associated with

objective measures of leg functioning in PAOD:

AAI = highest of DP/AT and PT/mean of both arms,

AAI = mean of DP/AT and PT/mean of both arms,

and AAI = lowest of DP/AT and PT/mean of both

arms.

The prevalence of PAOD, defined as an AAI 0.9,

ranged from a minimum of 47% when the first

formula was used to a maximum of 59% when the

third was used.31 In cases where the right and left

legs showed a difference of AAI, the lowest of these

correlated best with leg functioning. Moreover, the

lower AAI determined by ‘‘mean of DP/AT and PT/

mean both radial artery’’ was most predictive of

walking endurance and walking velocity in cases of

PAOD. The authors offered two potential explana-

tions for the finding that using the mean of the DP/

AT and PT systolic pressures is the optimal way to

calculate AAI when assessing lower extremity

functioning.

First, the mean of DP/AT and PT may best reflect

total perfusion of the more diseased lower

extremity and, second, when the two pressures are

averaged, the random variation and measurement

error intrinsic to measures of arterial pressure are

minimized, the result being a closer association of

the mean AAI with functioning.31 Hiatt et al.28

used two ways to calculate the numerator of the

AAI. Since the difference in systolic blood pressure

between the DP/AT and PT was found to have a

95% range of )21 to +10 mm Hg, the ‘‘mean of PT

and DP/AT’’ was used if PT and DP/AT differed no

more than )21 to +10 mm Hg. Alternatively, the

‘‘lower of PT and DP/AT’’ was used if PT and DP/AT

differed more than )21 to +10 mm Hg.

Since AAI may indicate the presence and, more

vaguely, the severity of PAOD without a high

sensitivity or specificity, only one standardized

formula should be used to calculate it. This may

keep its use simple and reproducible in varying

hospital and general practice settings. We strongly

advise against calculating AAI separately for each

lower leg artery since the sensitivity and specificity

of the AAI for detecting PAOD per artery is even

lower.92 Still, a large difference in pressure readings

between the DP/AT and PT in the same limb should

be considered indicative of PAOD.8,55 Hence, we

advise calculating AAI for each leg by measuring

the systolic pressures over both DP/AT and PT and

using their mean for the numerator as this reduces

the measurement bias and gives a good impression

of the total lower leg perfusion. Bias can further be

reduced by measuring the AAI twice per leg and

using the mean of both measurements for the

numerator.

Denominator. Furthermore, Hiatt et al.28,78

advised using the ‘‘mean of both arms’’ for the

denominator in cases where the difference in sys-

tolic blood pressure between the right and left arms

did not exceed the 95% range of )9 to +8 mm Hg.

Alternatively, they advised using the ‘‘higher of

both arms’’ for this if the brachial pressure of both

arms differed more than )9 to +8 mm Hg because

they assumed that there might be an arterial

occlusion on one side causing the difference.28,78

For reasons of simplicity, we advise measuring

the systolic pressures of both arms to detect possible

pressure differences indicating aortic coarctation or

brachial arterial stenosis. Because the systolic

pressure perfusing the body distal of the run-off of

the left subclavian artery is equal to that in the left

arm, the left brachial systolic pressure should be

used for the denominator, provided no brachial

arterial stenosis is found. Isolated stenosis of the left

subclavian artery, however, is very rare; and the

chance of having a left subclavian stenosis without

lower extremity involvement can be considered

naught.

In short, we advice calculating AAI separately

for each leg and using the formula AAI = mean of

DP/AT and PT/left brachial artery.

Cut-off Value of the Normal AAI

The lower cut-off point of the normal AAI indica-

tive of the absence of PAOD may importantly differ

from the upper cut-off point of an aberrant AAI

indicating the presence of PAOD (Tables II and III).

288 Klein and Hage Annals of Vascular Surgery

Typically, the AAI cut-off value for presence of

disease has been defined between 0.90 and

0.80,60,74 but it is obvious that there is – not in the

least due to differences in methods of AAI mea-

surement – no one fixed cut-off point indicating

the absence or presence of PAOD.

Varying the cut-off AAI may triple the sensitivity

of the test4,25 and double the estimates of PAOD

prevalence.28,38,59 Hiatt et al.78 included an exten-

sive table of lower limits of the normal range sub-

divided for the left and right legs, the PT and DP,

and the two sexes; and some (groups of) authors

even included estimations on the probability of

PAOD for a given AAI.54,63 Still, such differentia-

tion is hardly applicable in daily clinical practice.

The sensitivity and specificity of AAI cut-off

values to detect PAOD are 96% or higher when

using arteriography as the gold standard,24 and

subjects with a resting AAI of 0.94 or higher have

no arteriographic evidence of PAOD.4,24,55 Carter55

found 95% of patients without PAOD to have AAI

of 0.97 or higher, whereas all of his patients with

arteriographically proven PAOD had AAI lower

than that.

We recommend that 0.9 be accepted as the up-

per limit of an aberrant AAI and 1.0 as the lower

limit of a normal AAI. An AAI between 0.9 and 1.0

seems to be not conclusive and should lead to

further assessment. Future investigators should

state what AAI value was used as a cut-off point

since the sensitivity of the AAI for the presence of

PAOD depends on this.

To summarize, we feel that AAI reported in sci-

entific work should be assessed by experienced

observers. Assessment of AAI at rest in the supine

position is acceptable as the standard procedure.

Different sphygmometer cuffs ought to be used for

the arms and legs, both of which should have a

width of 1.5 that of the extremity at the level of

measurement. The cuff should be placed just

proximal to the malleoli to assess crural blood

pressures. A handheld pencil-Doppler device ought

to be used for measurement of both the brachial

and crural blood pressures. Measurements should

be performed at both arms and over the DP/AT and

PT of both legs, but the left arm pressure is pre-

ferred for use as the denominator. The mean of the

systolic pressures of the DP/AT and the PT ought to

be used for the numerator of the AAI for that leg.

However, difference in pressure readings between

the DP/AT and PT in the same limb should be

considered indicative of PAOD. Measurement bias

is further reduced by measuring AAI twice per leg

and using the mean of the two measurements. We

recommend accepting 0.9 as the upper limit of an

aberrant AAI and further assessing the arterial

status of all patients with an AAI between 0.9 and

1.0.

To allow for comparison of results from one

investigator to another without tremendous varia-

tions due to the different methods of assessment,

we urge future investigators to adhere to these

recommendations or to mention the circumstances

or methods of assessment and calculation of AAI in

the Method section of their report in cases where

these differ from those recommended. In these

cases, information on why the authors felt it better

to use an alternative method may further enhance

the possibilities of comparison with reports from

other research groups.

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