If Allen's test is negative, which action is appropriate before drawing an arterial blood gas?

• A. Use an alternate arterial site for ABG
• B. Recheck the test later
• C. Apply topical vasodilator
• D. Use venous sampling

Answer: (A)

Allen's test checks whether the hand has adequate collateral blood flow if the radial artery is used for arterial sampling. A negative (abnormal) result suggests insufficient collateral circulation, meaning cannulating the radial artery could put the hand at risk for ischemia. In that case, the safest choice is to use an alternate arterial site for the arterial blood gas, such as the brachial or another approved artery, following facility protocol. Rechecking later wouldn’t mitigate the immediate risk, a topical vasodilator isn’t a standard step for this scenario, and venous sampling wouldn’t yield arterial blood gas values.