In venipuncture collection, what is the purpose of the first 15-25 mL drawn?

• A. It is discarded as waste
• B. It is used to calibrate the centrifuge
• C. It is used to monitor sample quality
• D. It is used for testing and diverts blood most commonly contaminated by skin bacteria

Answer: (D)

The main idea is managing contamination from the skin during venipuncture. The skin around the puncture site carries bacteria, and the first blood that comes through the needle is most likely to pick up these skin microbes (and any residual antiseptic). By diverting the first 15–25 mL into a separate tube for testing or discard, labs can check for or minimize the impact of that initial contamination. The remaining blood then serves for the actual diagnostic tests with a lower risk of skin flora skewing results. This approach helps prevent false-positive findings due to skin contamination, which is especially important for cultures and other sensitive tests.