False-positive pregnancy test after passive transfusion of β-human chorionic gonadotropin from donor red blood cells during erythrocytapheresis

BACKGROUND: Patients transfused with blood products may passively receive soluble antibodies, proteins, and other analytes that persist during the collection, processing, and transfusion of the blood product. In this report, a female patient who received transfusion of five red blood cell (RBC) units during erythrocytapheresis later demonstrated an unexpected positive result in assays for the β-subunit of human chorionic gonadotropin (bHCG), a screening test for pregnancy. The result caused postponement of an elective surgical procedure. A follow-up test 1 week later was negative. STUDY DESIGN AND METHODS: To investigate the possibility of passive transfusion of the hormone from a donor RBC unit, a sample from each of the units transfused was assayed for the level of bHCG. RESULTS: One of the 5 units transfused to the patient had a high level of bHCG. The observed bHCG level in the recipient was found to be comparable to the predicted level, given the donor's plasma bHCG level and accounting for the dilution factors in the preparation of the RBC unit and the erythrocytapheresis procedure and the in vivo t_1/2 of the hormone. CONCLUSION: The donor, who was unaware of her pregnancy status at the time of donation, harbored a high bHCG level that caused the positive test result in the recipient patient's serum and urine. If an unexpected analyte or serology is detected in a recipient of a blood transfusion, it is important to consider the possibility of passive transfusion of the analyte.