If an EDTA tube is collected before a serum tube, what is the likely impact on the serum sample?

• A. Serum becomes hypercoagulable.
• B. EDTA carryover could contaminate the serum sample, falsely altering results.
• C. The sample coagulates immediately.
• D. Hemoglobin levels are increased in serum.

Answer: (B)

Carryover of additives between tubes is the key idea here. EDTA is a strong calcium chelator used in lavender-top tubes. If the EDTA tube is drawn first, residual EDTA can be carried into the next tube and contaminate the serum sample. That contamination introduces an anticoagulant into a sample that should have clotted, which can alter the serum’s chemistry and skew test results—especially those relying on calcium and other ions. In short, EDTA carryover can falsely change results because it changes the way the blood components behave during testing. The other options don’t fit because EDTA would not make the serum coagulate or become hypercoagulable; it would do the opposite by inhibiting clotting, and it doesn’t inherently cause a simple rise in hemoglobin.