Objective: This case report investigates an unusual hCG result in a woman who is not pregnant. Patient and methods: A 43-year-old woman was admitted for recurrence of thrombotic thrombocytopenic purpura (TTP) and therapeutic plasma exchange (TPE) was initiated. Prior to transitioning the patient from TPE to immunosuppressive therapy, a serum qualitative hCG test was performed and was positive. Several etiologies for elevated hCG were considered and investigated, including heterophile antibody interference, endogenous hCG from pituitary or malignancy, and exogenous hCG. Results: Retrospective measurement of hCG levels in remnant samples, including a sample obtained prior to TPE initiation, demonstrated that the hCG elevation occurred with plasma administration for TPE. Further investigation with the American Red Cross confirmed that a plasma donor was unknowingly pregnant and in the latter half of the first trimester at the time of donation, when hCG levels peak. Conclusion: In plasma recipients with unexplained hCG elevation, passive transfer of hCG from plasma should be considered in the differential diagnosis. Retrospective measurement of hCG in remnant samples obtained prior to plasma exchange can assist in confirming the source.