What is the anticoagulant of choice for blood gas analysis?

• A. EDTA
• B. Heparin
• C. Sodium fluoride
• D. Citrate

Answer: (B)

Preserving true blood gas values requires an anticoagulant that does not interfere with pH, pCO2, or pO2. Heparin is the preferred choice because it prevents clotting without significantly altering the gas tensions or electrolytes in the sample. In practice, blood gas samples are collected in heparinized syringes (often lithium heparin) to keep the blood fluid and accurate for immediate analysis. Other anticoagulants bind calcium or otherwise alter the chemistry of the sample; for example, EDTA and citrate chelate calcium and can shift acid–base status and gas results, making them unsuitable for blood gas analysis. Sodium fluoride on its own is not an anticoagulant and is used primarily with glycolysis inhibitors for glucose testing, not for preserving blood gas measurements.