When must a sample be obtained for pretransfusion testing?

• A. Only the day of transfusion is required
• B. If pregnant or previous transfusion, 3 months; otherwise day of
• C. Always 6 weeks prior
• D. Only after ABO typing

Answer: (B)

The important idea is that pretransfusion testing relies on an up-to-date assessment of a patient’s antibodies. After events like pregnancy or a transfusion, a patient may form new alloantibodies against red-cell antigens. Because antibodies can appear or change in the months after sensitization, using an old sample might miss these antibodies and lead to an incompatible transfusion.

Therefore, if a patient has had pregnancy or a prior transfusion, a new specimen should be obtained within a recent window (three months) to accurately detect any newly formed antibodies before transfusion. If there’s no such recent exposure, a sample drawn on the day of transfusion is acceptable for the testing required.

This ensures the antibody screen and crossmatch reflect the patient’s current immune status.