Which statement best describes the effect of EDTA carryover into serum tests?

• A. EDTA carryover could contaminate the serum sample, falsely altering results.
• B. Serum samples are unaffected by EDTA.
• C. EDTA carryover improves serum test accuracy.
• D. EDTA carryover only affects plasma tests.

Answer: (A)

EDTA carryover into serum tests matters because EDTA is a strong chelator of calcium and other divalent metal ions. If even a small amount of EDTA from a previous tube or sample remains in the serum, it binds calcium and related ions present in the assay. This reduces the free ion concentrations that many serum tests rely on, leading to falsely altered results (often falsely low calcium and potentially affecting other ion-dependent measurements). Serum should be free of anticoagulants, so contamination by EDTA will not improve accuracy and can skew results. It can affect serum tests just as it would affect plasma tests, so the idea that it only impacts plasma is incorrect.