Ace the NHCO Phlebotomy Exam 2026 – Get Ready to Draw Success!

Arterial blood gas testing is based on the actual gas tensions and acid-base status of arterial blood, which reflects lung gas exchange more accurately than venous blood. Tissues extract oxygen and produce carbon dioxide as blood circulates, so using venous blood would give incorrect values for oxygenation and CO2. Handling the sample anaerobically—using a heparinized syringe and minimizing contact with air—prevents gas exchange with the environment, preserving the true PaO2, PaCO2, and pH. Because of this, drawing from a vein is not appropriate, and samples should be analyzed promptly rather than left at room temperature for hours. Also, ABG specimens are collected in anticoagulated tubes to prevent clotting; claiming no anticoagulant is needed would be incorrect.