What risk is associated with drawing multiple tubes containing EDTA and heparin back-to-back?

• A. Cross-contamination of additives; can affect test results
• B. Increased clotting of the sample
• C. No risk
• D. Faster processing

Answer: (A)

Cross-contamination of additives between consecutive tubes is the key risk. When multiple tubes with different anticoagulants are drawn in sequence, trace amounts of one additive can be carried into the next tube through the needle, syringe, or cap. EDTA chelates calcium, which can alter calcium-dependent tests and affect hematology results, while heparin is used for plasma chemistry; any carryover can skew those measurements. Even tiny amounts can change test outcomes enough to mislead results. To minimize this, clinicians follow draw protocols that reduce carryover, such as discarding the initial blood after switching additives or using proper technique and order of draw. The other statements don’t describe this carryover mechanism and thus don’t capture the real risk.