"1.Elevate patients hand and ask him 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.
4.Ulnar pressure is released and the colour should return in 7 seconds.
If color returns as described above
the Allen's test is considered to be "positive."
If color fails to return
the test is considered "negative" and the ulnar artery supply to the hand is not sufficient. The radial artery therefore cannot be safely pricked/cannulated.
Allen's test is also performed prior to heart bypass surgery.
The radial artery is occasionally used as a conduit for bypass surgery
and its patency lasts longer in comparison to the saphenous veins. "