An altered test, first suggested byIrving S Wright in 1952, has almost universally replaced the original method in contemporary medical practice. The alternative method is often referred to as themodified Allen's test ormodified Allen test.[2]
The original test proposed by Allen is performed as follows:[1]
The patient is asked to clench both fists tightly for 1 minute at the same time.
Pressure is applied over theradial andulnar arteries simultaneously so as to occlude them.
The patient then opens the fingers of both hands rapidly, and the examiner compares the colour of both. The initialpallor should be replaced quickly byrubor.
The test may be repeated, this time occluding the ulnar arteries.
In the modified Allen test, one hand is examined at a time:[2]
The patient is asked to clench their fist for about 30 seconds.
Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.
Still elevated, the hand is then opened. It should appear blanched (pallor may be observed at the finger nails).
Ulnar pressure is released while radial pressure is maintained, and the colour should return within 5 to 15 seconds.
If color returns as described, Allen's test is considered to be normal. If color fails to return, the test is considered abnormal and it suggests that theulnar artery supply to the hand is not sufficient.[2]
The modified Allen's test is also performed prior toheart bypass surgery. Theradial artery is occasionally used as a conduit for bypass surgery, and its patency lasts longer in comparison to thesaphenous veins. Prior to heart bypass surgery, the test is performed to assess the suitability of the radial artery to be used as a conduit. A result of less than 3 seconds is considered as good and suitable. A result of between 3–5 seconds is equivocal, whereas the radial artery will not be considered forgrafting if the result is longer than 5 seconds.[3]
The utility of the modified Allen's test is questionable,[4] and no direct correlation with reduced ischemic complications of radial artery cannulation have ever been proven. In 1983, Slogoff and colleagues reviewed 1,782 radial artery cannulations and found that 25% of them resulted in complete radial artery occlusion, without apparent adverse effects.[5] A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test.[6][7] In addition, the results of Allen's tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections.[8][9]
Further modifications to the test have been proposed to improve reliability.[10]
^McGregor, AD (1987). "The Allen test – an investigation of its accuracy by fluorescein angiography".J Hand Surg Br Vol.12 (1):82–85.doi:10.1016/0266-7681(87)90065-9.PMID3572188.
^Stead, SW; Stirt, JA (1985). "Assessment of digital blood flow and palmar collateral circulation".Journal of Clinical Monitoring and Computing.2 (1):29–34.doi:10.1007/bf02915870.PMID3835222.S2CID39584943.
