Which sequence describes the Modified Allen's Test procedure?

• A. Occlude both radial and ulnar arteries, have the patient open and close the fist while maintaining pressure, release both arteries simultaneously
• B. Occlude only the radial artery, have the patient open and close the fist while maintaining pressure, then release both arteries
• C. Occlude both arteries, have the patient open and close the fist while maintaining pressure, release only the ulnar artery while the radial remains occluded, and blood flow should return within 10 seconds
• D. Occlude only the ulnar artery, then release the radial artery

Answer: (C)

The test is about evaluating collateral blood flow to the hand through the ulnar artery when the radial artery is blocked, which is crucial before relying on the radial artery for procedures. To perform it, both the radial and ulnar arteries are compressed at the wrist to blanch the hand. The patient then opens and closes the fist while pressure is held. After that, you release the ulnar artery while keeping the radial artery occluded. If color returns promptly, typically within about 10 seconds, it shows the ulnar artery can adequately perfuse the hand and that radial access would be safe. If color does not return quickly, collateral circulation is poor, signaling a higher risk with radial procedures.

The other sequences don’t isolate the collateral pathway in the same way: releasing both arteries at once doesn’t test one artery’s ability to supply the hand when the other is occluded; releasing only one artery after occluding both doesn’t specifically assess the ulnar pathway; and occluding only one artery initially fails to establish the baseline blanch and the subsequent assessment of collateral flow.