Abstract Aim: To compare the Allen’s Test with modified Allen’s Test and its clinical importance Materials and Methods: Thirty students from Saveetha Dental College, Chennai were selected for this experiment, people were chosen at randomn. The Allen’s test is a worldwide standardized test used to determine whether the patency of the radial or ulnar artery is normal. It is performed prior to radial cannulation or catheterisation, as placement of such a catheter may result in thrombosis. Allen’s test is considered to be normal. The patient is asked to clench both fists tightly for 1 minute at the same time. Pressure is applied over both radial 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 should be replaced quickly by rubor. The test may be repeated, this time occluding the ulnar arteries. In the modified Allen test, one hand is examined at a time, the hand is elevated and 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 colour returns as described. Results: There was no particular difference between the original Allen’s test and the modified Allen’s test. Conclusion: The Allen test is a good and valid screening test for the circulation of the hand. The test is therefore used to reduce the risk of ischemia to the hand. There has been renewed interest in radial artery bypass conduits for coronary artery revascularization, and surgeons should be familiar with methods of assessing circulation of the hand to determine which patients are candidates for this procedure. Thus, if the blood supply from one of the arteries is cut off, the other artery can supply adequate blood to the hand. A minority of people lack this dual blood supply. Keywords: Allen’s Test, Fist, ulnar artery, thrombosis, radial artery bypass conduits, catheterisation, revascularization, Modified Allen’s test, Hand haemodynamics, Collateral flow. Introduction The Allen test is a widely used screening method of hand circulation. The circulation of the hand is supported by two main arteries, ulnar artery and radial artery. 1 Allen’s test is also used to assess the adequacy of ulnar collateral circulation to the hand. Allen first described his test in 1929 but did not indicate a time period after which a test should be deemed positive. Various modifications have been suggested with differing time periods for a positive test ranging from 5 to 15 seconds. The possibility of hand ischemia after any intervention on the radial artery has made it imperative to establish the adequacy of the ulnar arterial collateral circulation to the hand. 2 Allen’s test is widely used to assess the ulnar collateral blood supply of the hand before radial artery harvest for coronary bypass surgery. The hand is normally supplied by blood from both the ulnar and radial arteries. To identify those patients at risk of ischemia a preoperative assessment of the ulnar collateral blood supply using Allen’s test is commonly practiced. There is, however, no consensus regarding the optimum cut-off time for a positive Allen’s test. 3 First described in 1929 by Edgar Allen, the Allen’s test has become the most common method for assessing palmar arch patency. 7 The original technique has been altered and is called the modified Allen’s test. 8 The modified Allen’s test is often used in the preoperative evaluation of the radial artery for coronary artery bypass graft to determine whether sufficient collateral circulation is present throughout the hand to allow harvesting. 9 Under such circumstances, the modified Allen’s test cannot be accurately per-formed and the radial artery is often catheterized with-out assessing the collateral circulation of the hand. 13 The Allen’s test was first described in 1929 to evaluate the arterial blood supply of the hand in patients with thromboangiitis obliterans. 12 Symptoms can vary from numbness, stiffness and coolness of the hand or digits to rarely rest pain from acute ischemia. 10 Blood flow in the largest arteries of the arm up to the digital arteries is numerically modelled using the one-dimensional equations of pressure and flow wave propagation in compliant vessels. 4 Materials and methods: Thirty students from Saveetha Dental College, Chennai were selected for this experiment. People were chosen randomly for this study. In the short duration that was given, the experiment was performed on the students. 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 both radial 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 should be replaced quickly by rubor. Fig 1. The Allen’s test. (A) The ulnar artery is located by palpation at the proximal skin crease of the wrist and then com- pressed. (B) With both arteries compressed the subject is asked to clench and unclench the hand 10 times. (C) The hand is then held open, ensuring that the wrist and fingers are not hyperextended and splayed out. The palm is observed to be blanched. (D) The ulnar artery is released and the time taken for the palm and especially the thumb and thenar eminence to become flush is noted.Fig 2. The Modified Allen’s test. In the modified Allen test, one hand is examined at a time. (E) The hand is elevated and the patient is asked to clench their fist for about 30 seconds. (F) Pressure is applied over the ulnar and the radial arteries so as to occlude both of them. (G) Still elevated, the hand is then opened. It should appear blanched (pallor may be observed at the finger nails. (H) 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 supply to the hand is not sufficient. This indicates that it may not be safe to cannulate or needle the radial artery. The test may be repeated, this time occluding the ulnar arteries. Allen’s test looks for abnormal circulation. If colour returns quickly as described above, Allen’s test is considered to demonstrate normal circulation. If the pallor persists for some time after the patient opens their fingers, this suggests a degree of occlusion of the uncompressed artery Results:In summary, the Allen’s test is a time-honored, simple and non-invasive test to assess arterial flow through the palmar arches of the hand. The Allen test, albeit being cheap and simple, has been criticized for being too unreliable and subjective, even to a degree that it should be removed in favor of more objective tests. The Allen test is a clinical test and, as such, a subjective measure, which contains several possible biases. Hence, we could see that there was no major difference between Allen’s test and modified Allen’s test. The blood flow was not affected and it was applicable to all age groups. The circulation was normal. A practical vision about modern technology is to be able to have a comfortable, practical and effective way to obtain information in order not to harm the patient and to ensure an effective instrument for beneficial impact for anesthetists.Discussion: Anatomy of the radial or ulnar artery per se is seldom a reason why radial artery is not suitable for harvesting. More often there is a circulatory deficit which can be measured as insufficient increase of ulnar flow, absence of reverse flow in radial stump or as a loss of blood pressure in digits. In our study 11.7% patients had a circulatory contraindication for radial artery harvest. Anatomical and circulatory changes often correlate which each other and 9% of our patients had both anatomical and circulatory contraindications. 1 The test tells us nothing about the vascular anatomy of the hand, only the functional circulatory status which is interpreted by the examiner, whose interpretation is based on experience that may vary considerably. 3 The use of the radial artery as a conduit for coronary bypass grafting is a routine procedure today. Ischaemic complications associated with the harvest of radial artery are rare but they have been reported. 5 There has been a debate whether the Allen test is a sufficient screening method to exclude patients with possibly compromised hand circulation. There are several reasons for insufficient ulnar hand circulation. The collaterals between the radial artery and the ulnar artery are several. Altogether there are four arches, two in the carpal area and two in the palmar area. The palmar arches, superficial and deep, are especially important. They have been studied in detail in several cadaver studies. 6 Modified Allen test (MAT) has traditionally been used to identify patients at increased risk from radial artery catheterization. MAT can be influenced by a number of factors including overextension of the wrist, skin tension over the ulnar artery, and operator error. 11 MAT is a simple and inexpensive tool, but it also has important limitations: it requires the cooperation of the patient for its correct performance and does not provide information about the vascular anatomy of the hand. 14 The goal of this test is to ensure adequate collateral supply to the hand, before sacrificing 1 of the 2 major arterial suppliers of the hand. 15 On a theoretical basis, if collateral circulation is not impaired, return to normal colour to the hand (better seen in palmar area) should be within 3 to 12 seconds, thus being called a “negative” or “normal” MAT. 16 If it does not, then it is called a “positive” or “abnormal” MAT, and no intervention should be performed on that radial artery. 17 Furthermore, most critically ill patients cannot cooperate for the performance of the test as described. 18 In summary, arterial puncture appears to be a safe procedure and its serious clinical complications are rare. 19 All means of Allen’s test at our disposal may be acceptable and the combination of multiple tests may increase the sensitivity and the specificity. 20 Conclusion:In summary, the Allen’s test is a time-honored, simple and non-invasive test to assess arterial flow through the palmar arches of the hand. Based on the results, we can see that Allen’s test works for everyone of all age groups. There was no big difference between Allen’s test and modified Allen’s test. Allen’s test does not affect the blood flow in any way. Those people who lack the dual supply are at much greater risk of ischemia. The risk can be reduced by performing the modified Allen’s test beforehand. People who have a single blood supply in one hand often have a dual supply in the other, allowing the practitioner to take blood from the side with dual supply. The modified Allen’s test is also performed prior to heart bypass surgery. We conclude that the Allen test is a good and valid screening test for the circulation of the hand.