The Modified Allen Test
1) The hand is elevated and the patient/person is asked to make a fist for about 30 seconds.
2) Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.
3) Still elevated, the hand is then opened. It should appear blanched (pallour can be observed at the finger nails).
4) Ulnar pressure is released and the colour should return in 7 seconds.
Inference: Ulnar artery supply to the hand is sufficient and it is safe to cannulate/prick the radial
If color does not return or returns after 7–10 seconds, the test is considered positive and the ulnar artery supply to the hand is not sufficient. The radial artery therefore cannot be safely pricked/cannulated.
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