Which anticoagulant is preferred for ABG analysis?

• A. EDTA
• B. Citrate
• C. Lyophilized lithium heparin
• D. No anticoagulant

Answer: (C)

For ABG analysis, the sought-after principle is to prevent blood from clotting without altering the gas tensions or acid–base status of the sample. The anticoagulant that achieves this best is a heparin-based option, because heparin inhibits clotting without binding calcium or interfering with CO2, pH, or electrolyte measurements. The lyophilized lithium heparin in a dry syringe is preferred because it minimizes dilution of the sample while still effectively preventing clotting, preserving the accurate pH, pCO2, and pO2 readings. In contrast, EDTA chelates calcium and can affect pH and electrolyte balance, and citrate also chelates calcium and can alter acid–base calculations; using no anticoagulant would allow clotting and invalidate the results.