What is Allen's test?
Allen's test is used to measure blood flow in the hands. It determines whether one or both of the two arteries - Ulnar and radial arteries - which bring blood to their hands is functional. The test was developed by Edgar van Nuys Allen, a doctor from the United States.
This procedure temporarily stops blood flow into the hands so that the doctor can see how long it takes for his hands to return to their normal color. The Allen test is usually performed before the introduction of the cannula tube or radial arterial blood to ensure that it does not disturb the blood flow in the hands.
The completion of the complete Allen test takes about a minute. First, the patient raises his hand to be tested above the heart level. Then the patient is asked to make a strong fist. This helps to remove blood from the hand. Then Ulnar and radial arteries are pressed hard enough so that the blood can not flow into the hand. After a few seconds, the arteries are released and the patient will be asked to release his hand.
If the normal color of the hand returns within five to seven seconds, both arteries give the blood to the hand and the test is negative. The test is positive if the hand returns to its normal color. The positive result suggests that only one artery supplies blood.
Allen's positive result means that it is not safe to draw blood or insert a cannula in the area. The test can be re -performed on the other side. It is rare that both hands show positive results.
Most patients have negative results when they pass Allen's test. Those who have a positive result usually have sufficient blood flow from one functional artery. The purpose of the test is to ensure that the flow or other intrusion into the artery does not stop the toe into the hand. It is also performed so that the doctor can avoid damage to a single functional artery in the hand.
both Ulnar and radial arteries are branches of brachial arteries. Ulnar is the larger of them. It runs just below the elbow to the palm. Radial artery runs from forearm and koIt also does in the palm.