Assessment of collateral hand circulation by modified Allen’s test in normal Indian subjects

Abstract

Background

Allen’s test (AT) and Modified Allen’s Test (MAT) are used as screening methods for assessment of the hand circulation. Few people lack the dual blood supply of hand and are at risk of hand ischemia after any intervention on radial artery. The Purpose of the study was to assess the collateral circulation of hand using MAT in normal Indian subjects and in elderly population to know the prevalence of positivity of Allen’s test.

Methods

900 participants (1800 hands) were divided in two groups. Group I had participants with age <50 years and group II had participants with age ≥50 years. MAT was performed in all participants and results were compared between the two groups.

Results

In group I (n = 450, 900 hands), 313 were males and 137 were females, with mean age of 35.04 years. The relative percentages of a normal, equivocal, borderline and abnormal MAT were 77.8%, 16.6%, 3.7% and 1.6%, respectively. In group II (n = 450, 900 hands), 248 were males and 202 were females, with mean age of 60.4 years. The relative percentages of a normal, equivocal, borderline and abnormal MAT were 69.0%, 18.6%, 6.60% and 5.66%, respectively. A positive/abnormal test was significantly more common (5.66% Vs 1.66%, P < 0.00001) in older group.

Conclusion

MAT is simple, time tested and non invasive test to assess collateral circulation of the hand. A negative MAT safely selects patients for radial artery harvest; however, if the test is positive and in older patients then a second objective test may be needed.

1. Introduction

The modified Allen’s test (MAT) is widely used as screening method for assessment of the hand circulation. The circulation of the hand is supported by ulnar and radial arteries which joins in the hand to forms palmar arches. Therefore, if one of the arteries is blocked due to intervention, the other artery can supply enough blood to prevent hand ischemia. This forms the basis of Allen’s test.¹ Few people lack this dual blood supply and are at risk of hand ischemia after any intervention on forearm arteries. It is crucial to establish the adequacy of the ulnar arterial collateral circulation to the hand when intervention on the radial artery is required.² This study was conducted to assess the adequacy of collateral circulation of hand using MAT in Indian population and comparing the collateral hand circulation in two groups of participants one <50 years of age and one ≥50 years of age.

2. Material and methods

This study was conducted at two tertiary referral centres by performing MAT on normal subjects. Institutional ethics committee approval was not required as it was observational study and consent from participant was implied as they all willingly participated in the study. Persons with a history of congenital hand anomalies, peripheral vascular diseases, diabetes/hypertension, hand/wrist trauma, previous radial artery cannulation were excluded. Patients who were uncooperative, unconscious and in whom interpretation of the test was difficult due to deep jaundice or dark pigmentation were also excluded.

The participants were divided in two groups. Group I had participants with age <50 years and group II had participants with age ≥50 years. 50 years was taken as cut off because signs of atherosclerosis start appearing at the age of 45 years in men and at 55 years in women. Since our study group involve both therefore we have taken 50 years as cut off. MAT was performed in all individuals in both groups and comparison of MAT was done between the two groups.

In Allen’s original test, both hands were tested concurrently compressing one artery of each hand simultaneously. But in MAT each hand is examined separately. The subjects were asked to sit comfortably and instructed not to hyperextend their fingers or wrist. The radial artery (RA) and ulnar artery (UA) are compressed lightly simultaneously using both the thumbs of examiner to occlude both the arteries at wrist level and the subject was asked to clench and relax his hand three times till palm became blanched. The hand was then slowly opened to a neutral position, and the examiner removed pressure from the ulnar artery. Time taken (in seconds) for the blanched hand to return to its normal colour was recorded by a stop watch. If the palmar arch is patent, than hand become pink within 3–9 s. If return of colour does not occur within 9 s this is called a positive MAT and is thought to preclude radial artery harvest. One experienced observer performed all of the tests. The result of modified Allen’s test was categorised as negative (up to 3 s), equivocal (3–6 s), borderline (6–9 s) and abnormal (>9 s).³

The proportional comparison between the two groups at different time intervals (Time taken for the blanched hand to turn pink) for two groups was done using chi-square (x²) test. A p value of <0.05 was taken as statistically significant.

3. Results

MAT was performed on 900 healthy volunteers (1800 hands). There were 561 male and 339 female with the age ranged from 18 to 90 years and average age was 47.72 years. These participants were divided in two groups. Group I had participants <50 years of age and group II had participants ≥50 years of age.

In group I there were 450 volunteers (900 hands). 313 were male and 137 were female with the age ranged from 18 to 50 years with average age - 35.04 years. 408 volunteers were right handed and 42 were left handed. In this group the MAT was negative (<3 s) in 701 hands, equivocal (3–6 s) in 150 hands, border line (6–9 s) in 34 hands and abnormal (>9 s) in 15 hands. In this group 368 volunteers had bilateral equal tests in both hands. In group II there were 450 volunteers (900 hands). 248 were male and 202 were female with the age ranged from 51 to 90 years with average age-60.4 years. 402 volunteers were right handed and 38 were left handed. In this group the MAT was negative (<3 s) in 621 hands, equivocal (3–6 s) in 168 hands, border line (6–9 s) in 60 hands and positive (>9 s) in 51 hands (Table-1). In this group 354 volunteers had bilateral equal tests in both hands. The percentages of a negative (up to 3 s), equivocal (3–6 s), borderline (6–9 s) and abnormal (>9 s) MAT was 77.8%, 16.6%, 3.7% and 1.6%, respectively in participants < 50 years of age. The relative percentages of a negative (up to 3 s), equivocal (3–6 s), borderline (6–9 s) and abnormal (>9 s) MAT was 69.0%, 18.6%, 6.60% and 5.66%, respectively in participants ≥ 50 years of age.

Table-1.

Results of MAT in different age groups.

S no.	Gender		Hand dominance		Allen’s test
	Male	Female	Right	Left	<3 SEC no of hands	3-6 SEC. no of hands	6-9 SEC no of hands	>9 SEC no of hands
MAT<50years of (n = 450)	313	137	408	42	701 (77.88%)	150 (16.66%)	34 (3.77%)	15 (1.66%)
MAT>50years of (n = 450)	248	202	402	48	621 (69.0%)	168 (18.66%)	60 (6.66%)	51 (5.66%)

The overall test was positive in 3.665% patients. The test positivity rate in younger persons was 1.66% and in older was 5.66% (p < 0.00001).

4. Discussion

Allen’s test (AT) was first described in 1929 to assess arterial blood supply and collateral circulation of the hand in patients with ischemia of the upper extremity especially for thromboangitis obliterans.⁴ The scientific rationale of AT stems from the fact that while Radial artery (RA) is easily palpable at wrist, Ulnar artery (UA) cannot be palpated; hence its patency and therefore the collateral circulation of hand cannot be assessed clinically. AT confirms that hand will remain perfused, via UA and palmar arch, if any access/intervention via RA results in its occlusion. AT was modified as MAT in the same year by Irving S. Wright, which is traditionally preferred over AT.⁵ WHO guidelines on best practices in phlebotomy suggest that MAT should be performed before taking an arterial sample.⁶ In addition, MAT, as an initial simple clinical test, is widely used to assess the arterial blood supply of the hand before harvesting a radial forearm flap, radial artery as a graft for bypass surgery, before catheterization of the radial artery for coronary angiography, making A-V fistula for haemodialysis, for various micro vascular surgeries and for diagnosis of vascular abnormalities of the upper limb and thoracic outlet syndrome.^{7, 8, 9}

MAT, however, has been criticized due to its subjective assessment with unclear cut-off values in literature, chances of false positives/negatives, requiring patient’s cooperation, assessment affected by hyperextension of the wrist or wide separation of the digits and variable arterial anatomy.^{10, 11, 12} Even more importantly, its diagnostic validity to serve as a screening tool for collateral circulation deficits in the hand and sensitivity of positive AT/MAT to predict adverse outcome after RA cannulation have been questioned by many large studies including a recent systemic review; which suggests that there is insufficient evidence to support its systematic use before arterial puncture.^{13, 14, 15, 16, 17, 18, 19, 20, 21} The critics also emphasize the extreme rarity (0.02–0.09%) of serious hand ischemia following radial access plus extensive experience of trans-radial angiographic procedures with outstanding safety outcomes – with or without any preoperative AT/MAT.^{22, 23, 24, 25, 26, 27, 28, 29}

On the other hand, proponents of MAT are supported by several large studies which have established the lack of vascular complications with a MAT cut-off point of up to 12 s.^27,30,31

In a study by Benit et al. ³of MAT on 1000 consecutive patients (mean age 62.3 years; range 28–90 years) undergoing cardiac catheterization recommended MAT before radial artery puncture. MAT has also been shown to correlate well with Doppler study of collateral circulation of hand and the occurrence of complications in Transradial Coronary Angiography.^26,32,33 In addition, a recent study objectively studied the perfusion in hand with Laser Doppler in subjects with Physiological and/or Pathological ATs and conclusively showed that patients with a abnormal AT have more chances of loss of dual hand supply and altered perfusion pattern than patients with a normal AT.³⁴

Several researchers have opted for the middle path in this debate and suggest strengthening the clinical evidence of a positive MAT with an additional, more objective test like Oximetry, Plethysmography, USG Doppler, Laser Doppler and Angiography etc.^{17,25,35, 36, 37, 38, 39, 40} These tests, although more objective than MAT, are not without their share of limitations, not to mention the extra cost and limited availability (Table 2).

Table-2.

Pros and cons of different techniques for assessment of hand’s collateral circulation.

S no	Tests	Pros	Cons
1	Modified Allen’s test	Simple, no cost	Subjective, false-positives/false-negatives
2	Doppler plethysmography	objective evaluation/documentation of patency of the major arteries of hand severely abnormal findings are obvious	provides no information on the morphology of the artery will not identify anatomic variants time-consuming no absolute value for the normal response in the amplitude of the waveform with radial artery compression change in oscillation is subjective and not easily quantifiable
3	Doppler digital pressures and waveforms	Simple, objective test little extra cost severely abnormal pressures are obvious	provides no information on the morphology of the artery no identification of anatomic variants no agreement as to what is considered a significant drop in pressure
4	Duplex ultrasonography	allows mapping of the entire vessel size, morphology, flow velocity and direction good for viewing stenotic or calcified artery good for identifying anatomic variants	more expensive equipment (scanner) required clenching of the fist may affect the characteristics of the Doppler waveform
5	Pulse oximetry	simple, adds little extra cost	amplitude of the waveform may vary on which finger the probe is placed and the proximity of the probe to the arterial source room temperature may affect reading
6	Laser Doppler flowmetry	accurate, quick, and non-invasive	High cost
7	Angiography	Gold standard	Invasive, cost involved

In his original description, Allen had described the findings of test as radial and/or ulnar arteries either patent or occluded and no time limit for blushing of the palm was described.⁴ Unfortunately, to date there is no consensus on nomenclature of test’s outcome (abnormal test is described as negative and normal test as positive test and vice versa) and optimum cut-off time for a positive/abnormal MAT which has been described from 5 to 15 s; leading to problem in documenting the results. Therefore we recommend standardization of MAT as – time for return to normal colour to the hand should be within 3–10 s, it should be called as a “negative” or “normal” MAT. If it does not, then it should be called a “positive” or “abnormal” MAT.

In our study of 1800 hands, MAT was positive in 3.665% patients. The test positivity rate in younger subjects (<50 years of age) was 1.66% as compared to 5.66% in older subjects (≥50 years of age). In patients with age >50yeras there is high possibility of atherosclerosis which may involve the radial artery. Therefore any patients with age >50 years had the more possibility of abnormal Allen’s test. This favours the rationale of using MAT as a preliminary screening test as most patients requiring access to RA are elderly.

While the debate about accuracy of AT/MAT in assessing ulnar artery patency and collateral circulation rages on; there is no denying the fact that it is a simple clinical test which provides information about RA and UA.⁴¹ Additionally, a positive AT predict underlying pathological conditions in patients with known Peripheral arterial disease better than negative AT in predicting normal anatomy. If AT is positive in presence of PAD, it is indicative of underlying RA/UA stenosis and catheterization of RA should be avoided.⁴² Combining MAT with Doppler ultrasonography can validate it as a tool for primary screening and objectively assess the absence of reverse flow in the superficial palmar branch or in the dorsal digital artery to the thumb upon radial artery occlusion which represents absolute contraindications to radial artery harvest.^43,44

5. Conclusion

MAT is a simple, least expensive, time tested and non-invasive test to assess collateral flow of the hand. MAT can be used as a screening test when any procedure on radial artery is planned. A negative MAT safely selects patients for radial artery access/harvest; however, if the test is abnormal combining it with Doppler ultrasound will further validate the findings. The overall test was positivity was significantly higher in older (>50 years) population which are more likely to have intervention on radial artery therefore it is advisable to perform MAT in these patients before intervention on radial artery.

Author’s contribution

Tanishq Agarwal- Formal analysis; Investigation; Methodology; Roles/Writing - original draft; Writing - review & editing.

Vrinda Agarwal- Formal analysis; Investigation; Methodology; Roles/Writing - original draft; Writing - review & editing.

Prof. Pawan Agarwal- Conceptualization; Formal analysis; Investigation; Methodology; Roles/Writing - original draft; Writing - review & editing.

Dr Sharad Thakur- Formal analysis; Investigation; Methodology; Roles/Writing - original draft; Writing - review & editing.

Dr Rajesh Bobba- Formal analysis; Investigation; Methodology; Roles/Writing - original draft; Writing - review & editing

Prof. Dhananjaya Sharma- Formal analysis; Investigation; Methodology; review & editing.

Declaration of competing interest

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.