Allen’s test is often used to assessed the efficacy of collateral circulation in the hand through the superficial and deep palmar arches. It is done prior to radial artery cannulation for pressure monitoring, diagnostic coronary angiography and coronary interventions. Modified version of Allen’s test using pulse oximetry and plethysmography is known as Barbeau test.
Initial description of Allen’s test was for the evaluation of patency of the circulation of the hand in thromboangiitis obliterans (Buerger disease) . In the original Allen’s test both hands are tested simultaneously and compared while in the modified Allen’s test, only one hand is tested at a time.
Barbeau test utilises pulse oximetry and plethysmography to assess the palmar arches . They reported that this method is more sensitive than modified Allen’s test. Using their method only 1.5% of patients were not suitable for radial approach modified Allen’s test excluded 6.3% were excluded. A good illustration of typical plethysmography tracings in the 4 types of responses (types A, B, C, D) are illustrated in the free full text article by Kotowycz MA et al . Patients with type D response (complete absence of plethysmography tracing at 2 minutes of radial compression) should not undergo transradial catheterization of that wrist.
In Barbeau test, pulse oximeter is placed on the ipsilateral thumb and the plethysmography tracing noted. The radial artery is then compressed for occlusion and change in tracing noted. Pulse oximeter reading is also noted: if constant reading is noted, it is positive pulse oximetry and if no reading is found it is negative pulse oximetry. The response of plethysmography is classified into 4 types:
Type A: There is no change in plethysmography tracing through out the 2 minutes of occlusion.
Type B: There is an initial drop in the amplitude which recovers fully at 2 minutes of occlusion.
Type C: Tracing becomes a straight line on radial artery occlusion, but recovers partly to a low amplitude tracing at 2 minutes of occlusion
Type D: Tracing becomes a straight line on radial artery occlusion and remains so throughout.
There is uninterrupted arterial filling during radial occlusion in types A and B. Recruitment of collaterals is probably the reason for type C response with delayed appearance of pulsatile tracing. These patients could be excluded from radial catheterization based on conventional modified Allen’s test. Patients with type D response do not have pulsatile collateral flow and are excluded from radial catheterization. Authors reported that using this method, they did not have a single case of hand ischemia in over 7000 patients undergoing transradial procedures at their institution.
Allen EV. Thromboangiitis obliterans: methods of diagnosis of chronic arterial lesions distal to the wrist with illustrative cases. Am J Med Sci. 1929;178 (3): 165–189.