Why must the order of draw be followed to prevent additive carryover that could affect results?

• A. To prevent cross-contamination of additives from one tube to another, which can alter test results
• B. To prevent needle-stick injuries
• C. To ensure tubes are filled to the correct volume
• D. To minimize sample hemolysis

Answer: (A)

Additive carryover is the risk that residual substances from one collection tube could enter the next tube and alter the test results. Each tube uses a specific additive to preserve or prepare the blood for particular tests, so if there’s any contamination from the previous tube, it can skew the measurements. For example, EDTA in a lavender tube contains potassium and chelates calcium; even tiny amounts carried into the subsequent tube can make potassium appear falsely high and calcium appear falsely low in the next specimen. Following the prescribed order of draw reduces the chance that an additive from an earlier tube ends up in the next one, protecting the integrity of each test result. The other concerns—such as safety from needle-stick injuries, ensuring correct fill volume, or minimizing hemolysis—are handled by different aspects of collection practice and aren’t about preventing additive carryover.