For CVA collection, how much initial volume should be discarded?

• A. 1-2 mL
• B. 2-4 mL
• C. 3-5 mL
• D. 6-8 mL

Answer: (C)

When drawing from a CVA line, you need to discard part of the blood to clear the catheter of IV fluids and any anticoagulant that could dilute the sample. The goal is to obtain a true sample of the patient’s circulating blood, not the fluid remaining in the line. The volume to discard corresponds to the catheter’s dead space, which for most CVA catheters is about 3 to 5 mL. Discarding this amount removes line contents and yields accurate analyte measurements; discarding too little risks dilution from the line, while discarding more than necessary wastes blood without added benefit.