The ulnar artery is the first choice for drawing an ABG specimen.

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The first choice site for drawing an ABG specimen is the radial artery, not the ulnar. The radial artery at the wrist is typically preferred because it lies close to the skin, is easy to palpate, and allows for straightforward compression after the puncture, which helps control bleeding and reduce complications. Before using the radial site, clinicians often perform an Allen test to ensure that the ulnar artery can adequately supply the hand if radial flow is compromised, providing a safety check for collateral circulation. The ulnar artery, while a potential alternate site, is deeper and less accessible, making puncture and hemostasis more challenging and increasing the risk of local complications or nerve injury. If the radial site is unavailable or contraindicated, other sites like the brachial or femoral arteries may be considered, but with higher risk profiles.