Before performing an arterial blood gas (ABG) sampling from the radial artery, the Allen test is conducted to assess the patency of the ulnar artery. A positive test confirms adequate collateral circulation. Which of the following indicates a positive Allen test?

1. A

   Patient complains of numbness and irritation

2. B

   After releasing pressure, blood flow returns within 3-5 seconds

3. C

   After releasing pressure, blood flow returns in 1-2 minutes

4. D

   None of the above

Appeared in: NORCET 6 mains-2024

Explanation

Listen in Hindi

• A positive Allen test confirms adequate collateral blood flow from the ulnar artery to the hand.
• The standard criterion for a positive test is the return of normal color (flushing) to the palm within 3-5 seconds after releasing pressure on the ulnar artery.
• This rapid reperfusion indicates that the ulnar artery can sufficiently supply the hand if the radial artery becomes occluded.
• This is a critical safety check to prevent ischemic injury to the hand following radial artery cannulation.

Why Other Options Were Wrong

• Option A: Numbness and irritation are subjective symptoms of ischemia or nerve compression, not the objective visual sign of reperfusion that defines a positive Allen test.
• Option C: A return of blood flow in 1-2 minutes is an extremely delayed response and indicates a negative Allen test, signifying severe ulnar artery insufficiency.
• Option D: This option is incorrect because a correct description of a positive Allen test is provided in another option.

Related Visual

Clinical Relevance

• Nursing practice connection: Knowing Allen test procedure and interpretation for ABG sampling helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• The Allen test is a fundamental nursing assessment to ensure patient safety before invasive procedures on the radial artery, such as ABG sampling or arterial line insertion.
• Failure to perform or correctly interpret the Allen test can lead to a serious complication: hand ischemia, which can result in tissue damage, loss of function, or even necrosis if the radial artery becomes thrombosed.
• What if? If a patient is unconscious and cannot make a fist, the nurse can still perform the test by elevating the hand and allowing gravity to assist in blanching before occluding the arteries. The rest of the procedure remains the same.

How to Approach the Question

• First, identify the core subject of the question: the Allen test.
• Recall the purpose of the Allen test: to check for collateral circulation via the ulnar artery before puncturing the radial artery.
• Understand the terminology: a 'positive' test in this context is a good sign, meaning the test was passed and the procedure can go ahead safely.
• Evaluate each option against the known criteria for a positive test. A positive result is defined by a rapid return of blood flow.
• Eliminate options describing negative results (delayed return of color) or unrelated symptoms (numbness). The option describing a rapid return of color (3-5 seconds) is the correct definition.

Concept Tested & Keywords

• Concept Tested: Allen test procedure and interpretation for ABG sampling.
• Stem keywords: arterial blood gas (ABG), radial artery, Allen test, ulnar artery, collateral circulation
• Lead-in keywords: indicates a positive Allen test
• Negative lead-in flag: false

Question ID

QcqnOSBSavInOvbuLXiGI6

Copy ID

Reference Book

E6 Anatomy Grays 43e Vol 2 Part 2 p. 73-75

E6 Medicine Harrison 22e Part 1 p. 1903-1905