Allen’s test checks blood flow to the hands by determining if both the ulnar and radial arteries are functional. The patient raises their hand, makes a fist, and the arteries are pressed to stop blood flow. If the hand returns to normal color within 5-7 seconds, both arteries are functional. If it takes longer, only one artery is functional and the test is positive. This means it’s not safe to draw blood or insert a cannula. The test ensures that a puncture or intrusion into an artery does not cut off blood flow to the hand.
Allen’s test is used to measure blood flow in the hands. It determines whether one or both of the two arteries – the ulnar and radial arteries – that carry blood to the hands are functional. The test was developed by Edgar Van Nuys Allen, a doctor from the United States of America.
This procedure temporarily cuts off blood flow to your hands so your doctor can watch how long it takes for your hands to return to their normal color. Allen’s test is typically done before cannula tube insertion or radial arterial blood sampling to ensure they don’t cut off blood flow to the hands.
Allen’s comprehensive test takes about a minute to complete. First the patient raises the hand to be tested above the level of the heart. Then the patient is asked to make a strong punch. This helps remove blood from the hand. Then the ulnar and radial arteries are pressed hard enough so that blood cannot flow into the hand. After a few seconds, the arteries are released and the patient will be asked to relax their hand.
If the normal color of the hand returns within XNUMX to XNUMX seconds, then both arteries are supplying blood to the hand and the test is negative. The test is positive if it takes more than seven seconds for the hand to return to its normal color. A positive result indicates that there is only one artery supplying blood to the hand.
An Allen test with a positive result means it’s not safe to draw blood or insert a cannula into the area. The test can be repeated in the other hand. It is rare for both hands to show positive results.
Most patients have negative results when they undergo Allen’s test. Those who have a positive result usually get sufficient blood flow from the only functioning artery. The purpose of the test is to ensure that a puncture or other intrusion into an artery does not cut off blood flow to the hand. It is also conducted so the doctor can avoid damaging the only functional artery in the hand.
Both the ulnar and radial arteries are branches of the brachial artery. The ulnar is the larger of the two. It goes from just below the elbow to the palm. The radial artery runs from the forearm and also ends in the palm.
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