What indicates a positive result in the modified Allen test?

A positive result in the modified Allen test is indicated when the oxygen saturation (SAO2) reading returns to its original value. This test assesses the collateral circulation in the hand, particularly focusing on the ulnar artery's ability to supply blood to the hand when the radial artery is temporarily occluded.

In the context of the test, the original SAO2 reading serves as a baseline for measuring the adequacy of blood flow through the ulnar artery once the radial artery is released. A return to the baseline value suggests that the ulnar artery is capable of providing sufficient blood supply, thereby confirming that collateral circulation is intact and functioning properly.

The other options do not indicate a positive result in the modified Allen test. For instance, if the skin color remains pale, it suggests inadequate blood flow, which is not a positive outcome. Numbness experienced by the patient may indicate nerve trauma or ischemia, which again does not confirm effective collateral circulation. A weak pulse would also indicate potential issues with blood flow. Thus, the return of the SAO2 reading to its original level is the key indicator of a positive result, reflecting proper perfusion through the collateral pathways.