1. Prepared by Kevin H. Toomer, MD, PhD
Reviewed by: Lorraine Blagg, MA, MLS(ASCP)CMSBB

Clinical vignette:A middle aged patient with no past medical history presented for volunteer blood donation. ABO/Rh typing results were as follows:

No historic ABO/Rh typing was available for comparison. The patient had a recent appointment with his primary care physician. Labs from that visit, including complete blood count, were unremarkable. Front type was repeated after washing patient RBCs, and the results were unchanged.

Question:Assuming laboratory error can be excluded, which of the following is the most likely explanation for these findings?