The anticoagulant of choice for arterial blood gas measurements is ______ in the ______ state.

• A. Lithium heparin; dry
• B. EDTA; dry
• C. Potassium oxalate; liquid
• D. Sodium citrate; dry

Answer: (A)

Arterial blood gas measurements depend on a sample that remains unclotted while preserving the true gas tensions and pH, without any dilution or interference from the anticoagulant. Lithium heparin provides reliable anticoagulation for this purpose and, in a dry state, minimizes any dilution of the blood by the anticoagulant solution. This keeps pH, PCO2, and PO2 readings accurate. Other anticoagulants, like EDTA, citrate, or oxalate, can chelate calcium or otherwise alter acid–base balance and electrolytes, and using liquid forms would introduce even more dilution, skewing the results. Therefore, the best choice is lithium heparin in a dry state.