The Allen's Test: Can I Get Phalloplasty With An Abnormal Result?
Preoperative Evaluation of Blood Flow In the Radial Forearm Free Flap
If you've been considering Radial Forearm Flap (RFF) Phalloplasty surgery, you may have heard of the Allen's test. The Allen's test is a simple and painless way to evaluate blood flow to the hands before surgery takes place. The result of the test can be either normal or abnormal, and it's important to know that an abnormal result doesn't necessarily preclude you from being a good candidate for RFF Phalloplasty.
The Allen's test is performed during the planning stage of RFF Phalloplasty. The hand of the donor arm is elevated and the patient is asked to clench their fist. Pressure is applied to both the ulnar and radial arteries to block blood flow, which causes the hand to blanch. When pressure on the ulnar artery is released blood flow is restored causing color to return to the hand. This is an indication that the ulnar artery has sufficient circulation to provide blood flow to the hand without the radial artery. When pressure on the ulnar artery is maintained but the radial artery is released, color returning to the hand is an indication that the radial artery has adequate circulation to be transferred with the free flap to the groin to provide blood flow for the phallus. An Allen's test is considered abnormal when color doesn't return to the hand after release of an artery after 10 seconds.
While not common there are some cases where an abnormal Allen's test result indicates a circulation problem and the other forearm or an alternate donor site has to be used. This can be very upsetting for patients who would strongly prefer to use one arm over the other, want to use the RFF donor site specifically, or who may not be suitable candidates for other donor sites. However, an abnormal Allen's test result doesn't definitively exclude use of the radial forearm flap.
If an Allen's test result is abnormal, the Phalloplasty surgeons at San Francisco's Buncke Clinic will employ a "surgical Allen's test" to determine whether radial forearm flap harvest is safe. An initial incision is made at the inner wrist to allow access for direct blocking of the radial artery with a vascular clamp so that blood flow to the hand can be evaluated prior to committing to raising the flap. From 2016 to 2018, only four out of 123 patients (3.3%) had an abnormal Allen's test result on their preferred donor arm. Each had a surgical Allen's test performed, which produced normal test results, and surgery proceeded as originally planned.
Blood flow issues with Phalloplasty can be devastating and require emergency surgical intervention. The standard Allen's test is commonly used to predict blood flow preoperatively but isn't always reliable, sometimes producing false abnormal results that can derail an established surgical plan. In the absence of more reliable but less invasive testing, the surgical Allen's test is an important tool for verifying blood flow prior to flap harvest.
References
An abnormal clinical Allen's Test is not a contraindication for free radial forearm flap
Travis J. Miller, Bauback Safa, Andrew J. Watt, Mang L. Chen, and Walter C. Lin. Clin Case Rep. 2020 Nov; 8(11): 2191–2194.
The clinical Allen's test should not be an absolute contraindication to FRF phalloplasty. Intraoperative radial artery exposure for a surgical Allen's test may be a useful tool to assess for candidacy for FRF flap in select patients willing to undergo a radial artery cutdown. Alternative testing modalities with high specificity would be desirable to avoid such an invasive diagnostic test and should be investigated in more detail.
Last updated: 04/19/22