Which statement about complement preservation in compatibility testing is correct?

• A. It is preserved by using fresh serum (less than 48 hours old).
• B. Complement is not needed for compatibility testing.
• C. Complement is destroyed by fresh serum.
• D. It is preserved by extending serum storage beyond 72 hours.

Answer: (A)

In compatibility testing that relies on the complement system, having active complement is essential for the assay to work. Complement is a heat-labile component in serum that enables lysis of target cells when antibodies are present. Because its activity declines with time and storage, using fresh serum ensures the complement is still functional. Typically, serum should be used within about 48 hours to preserve this activity; storing serum longer—especially beyond a few days or after multiple freeze-thaw cycles—reduces or inactivates complement, risking false results. That’s why using fresh serum less than 48 hours old preserves complement and provides reliable compatibility testing outcomes.