Learn all about Allen test, the test is named after Edgar Van Nuys Allen. Allen’s test or the Allen test is a medical sign used in physical examination of arterial blood flow to the hands. It was named for Edgar Van Nuys Allen, who described the original version of the test in 1929. 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.
The femoral artery is the least preferred arterial sampling site because it is a relatively deep artery; it lies adjacent to the femoral nerve and vein; and it does not have collateral blood flow. Puncture of the femoral artery is usually reserved for emergent situations or for the severely hypotensive patient who has poor.
Symptoms can vary from numbness, stiffness and coolness of the hand or digits to rarely rest pain from acute ischemia. It is important to note that not all patients found to have radial artery occlusions become symptomatic peripheral perfusion.
The Allen test can be used as a diagnostic tool for a number of disorders, such as any diseases with reduced vascularisation in the arm, i.e. thoracic outlet syndrome or compartment syndrome. A negative Allen’s test safely selects patients for radial artery harvest, although the cut-off point is controversial. However, if the test is positive, then a 2nd test such as dynamic Doppler ultrasound or measurement of digital pressure changes with radial artery occlusion may allow safe harvest.
This test is great at assessing blood flow, because when the pressure is applied to both arteries, blood is limited in its ability to enter the hand. With the repetitive opening and closing of the hand, the blood is pushed out of the hand, which explains it white/pale color. At the point where the tester removes pressure from one artery, the only pathway for blood to enter the hand becomes that artery, so any return of color (blood) to the hand signifies good blood flow in that artery.
What is Allen test
The Allen 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. The test is therefore used to reduce the risk of ischemia to the hand. The Allen test can also be used preceding the removal of the radial artery for a coronary bypass graft. It is done by simultaneous compression of both the radial and ulnar arteries, followed by exsanguination of blood from the palm by repeated clenching and unclenching of the fist. The pressure over the ulnar artery is then released while maintaining pressure over the radial artery. A 5–6 second delay in flushing of the palm suggests abnormal ulnar-artery patency.
Allen test Procedure
The procedure for performing a modified Allen’s Test is as follows:
- Instruct the patient to clench his or her fist; if the patient is unable to do this, close the person’s hand tightly.
- Using your fingers, apply occlusive pressure to both the ulnar and radial arteries, to obstruct blood flow to the hand.
- While applying occlusive pressure to both arteries, have the patient relax his or her hand, and check whether the palm and fingers have blanched. If this is not the case, you have not completely occluded the arteries with your fingers.
- Release the occlusive pressure on the ulnar artery. You should notice a flushing of the hand within 5 to 15 seconds. This denotes that the ulnar artery if patent and has good blood flow. This normal flushing of the hand is considered to be a positive modified Allen’s test. If the hand does not flush within 5-15 seconds, it indicates that ulnar circulation is inadequate or nonexistent; in this situation, the radial artery supplying arterial blood to that hand should not be punctured. This is called Negative modified Allen test.
Allen test Results
Among the 71 hands, 4 (5.6%) had an abnormal Allen test result (>10 seconds). Seven (10.6%) of 66 superficial palmar branches of the radial artery, 3 (4.2%) of 71 ulnar arteries, and 2 (2.8%) of 71 dorsal digital thumb arteries showed no flow with radial artery compression, as measured by Doppler ultrasonography.
Allen test Types
Allen test is of two types;
- Original test; the original test was modified in the early 50’s to fit as an evaluation of the collateral circulation before arterial cannulation
- Modified test; in the modified Allen test, one hand is examined at a time. A modified Allen’s test (MAT) is commonly used to assess palmar arch collaterals. A variety of non-invasive methods including digital pressures, plethysmography, pulse oximetry and duplex ultrasonography are available to supplement physical examination.
Allen test Positive
A positive Allen Test shows that the patient does not have a dual blood supply to the hand, which is a negative indication for catheterisation or removal of the radial arteries. Flushing is a positive Allen’s test. Ulnar artery can supply blood flow if radial artery is damaged or becomes occluded during the procedure. When the hands and fingers flush within 15 seconds, a positive Allen’s test, arterial puncture can be done.