Buerger's test is used to assess the adequacy of the arterial supply to the leg. It is performed in two stages.
With the patient supine, elevate both legs to an angle of 45 degrees and hold for one to two minutes. Observe the color of the feet. Pallor indicates ischaemia. It occurs when the peripheral arterial pressure is inadequate to overcome the effects of gravity. The poorer the arterial supply, the less the angle to which the legs have to be raised for them to become pale.
Then sit the patient up and ask them to hang their legs down over the side of the bed at an angle of 90 degrees. Gravity aids blood flow and colour returns in the ischaemic leg. The skin at first becomes blue, as blood is deoxygenated in its passage through the ischaemic tissue, and then red, due to reactive hyperaemia from post-hypoxic vasodilatation.
Both legs are examined simultaneously as the changes are most obvious when one leg has a normal circulation.