Corpus: Allen test

The Allen test is a clinical functional test used to assess blood flow to the hand via the radial and ulnar arteries.

In the palm, blood supply is provided by the superficial and deep palmar arches. Ideally, these vascular arches form anastomoses between the ulnar and radial arteries. However, the superficial palmar arch, which primarily originates from the ulnar artery, connects to the radial artery in only 42% of individuals. If this connection is absent, the superficial palm is not supplied by the ulnar artery. Additionally, if there are no anastomoses between the deep palmar arch and the radial artery, or if these connections are blocked (e.g., due to atherosclerosis), the hand lacks a collateral blood supply.

The Allen test is performed:

• as part of the functional assessment of peripheral arterial disease (PAD)
• for an initial evaluation of collateral circulation before radial artery puncture, e.g., for arterial blood sampling or prior to a cardiac catheterization
• before using the radial artery for coronary artery bypass surgery

Since thrombosis is a potential complication of arterial puncture, radial puncture should only be performed if adequate blood supply to the hand via the ulnar artery is ensured.

• The patient holds their hand upright.
• The examiner applies firm pressure to both the radial and ulnar arteries at the wrist, temporarily stopping blood flow to the hand.
• The patient is instructed to open and close their hand several times to accelerate the process. If the arteries are properly compressed, the palm appears pale.
• The examiner releases pressure from one artery while maintaining compression on the other and observes whether normal blood flow is restored. The hand should quickly regain its normal pink color.
• The test is then repeated for the other artery.

In a healthy individual, either the radial or ulnar artery alone should be sufficient to maintain blood supply to the hand.

• "Negative" Allen test: After releasing an artery, the hand regains its normal color within 5–7 seconds, indicating adequate collateral circulation.
• "Positive" Allen test: Delayed or absent reperfusion suggests vascular abnormalities or arteriosclerotic changes.