medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

, Allen's test or the Allen test is a

medical sign Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

used in

physical examination In a physical examination, medical examination, clinical examination, or medical checkup, a medical practitioner examines a patient for any possible medical signs or symptoms of a Disease, medical condition. It generally consists of a series of ...

arterial blood Arterial blood is the oxygenated blood in the circulatory system found in the pulmonary vein, the left chambers of the heart, and in the artery, arteries. It is bright red in color, while venous blood is dark red in color (but looks purple through ...

flow to the hands. It was named for Edgar Van Nuys Allen, who described the original version of the test in 1942. An altered test, first suggested by Irving S Wright in 1952, has almost universally replaced the original method in contemporary medical practice. The alternative method is often referred to as the modified Allen's test or modified Allen test.

Method

Original test

The original test proposed by Allen is performed as follows: # The patient is asked to clench both fists tightly for 1 minute at the same time. # Pressure is applied over the radial and ulnar 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 initial

pallor Pallor is a pale color of the skin that can be caused by illness, emotional shock or stress, stimulant use, or anemia, and is the result of a reduced amount of oxyhaemoglobin and may also be visible as pallor of the conjunctivae of the eye ...

should be replaced quickly by rubor. # The test may be repeated, this time occluding the ulnar arteries.

Modified test

In the modified Allen test, one hand is examined at a time: # 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 the

ulnar artery The ulnar artery is the main blood vessel, with oxygenated blood, of the Human Anatomical Terms#Anatomical directions, medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins ...

supply to the hand is not sufficient.

Significance

The modified Allen's test is also performed prior to heart bypass surgery. The

radial artery In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm. Structure The radial artery arises from the bifurcation of the brachial artery in the antecubital fossa. It runs distally on the anterior part of the ...

is occasionally used as a conduit for bypass surgery, and its patency lasts longer in comparison to the saphenous 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 for

grafting Grafting or graftage is a horticulture, horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the roots ...

if the result is longer than 5 seconds. The utility of the modified Allen's test is questionable, 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. A number of reports have been published in which permanent ischemic sequelae occurred even in the presence of a normal Allen's test. In addition, the results of Allen's tests do not appear to correlate with distal blood flow as demonstrated by fluorescein dye injections. Further modifications to the test have been proposed to improve reliability.

References

{{Cardiovascular system symptoms and signs Diagnostic intensive care medicine Diagnostic surgery Symptoms and signs: Vascular