The Scianna (Sc) blood group system comprises 7 high-prevalence and 2 low-prevalence antigens. To date, only very few examples of SC1- and SC3-autoantibodies have been reported, requiring the use of rare test cells, antisera, or immunoblotting for their identification in addition to absorption methods to exclude additional alloantibodies. Detection of an autoanti-Scianna using recombinant blood group antigens (rBGAs) has not been previously described.

Blood from a 85-year-old, not previously transfused male with carcinoma of the prostate was sent for antibody workup. Initial tests on an automated analyzer (Ortho Vision) included blood type, antibody screening tests (saline, indirect antiglobulin test (IAT), and with ficin-treated cells), autocontrol, and monospecific direct antiglobulin test (DAT). Antibody differentiation was done with plasma and eluate (BAG-Elutions-Kit) in the IAT and with papain-treated test cells (BioRad ID system). Plasma and eluate were treated with single soluble rBGAs (Ch, Rg, Kn^a, Yt^a, Sc1; inno-train Diagnostic GmbH, Kronberg, Germany) according to the manufacturer's instruction. Taq-cycle sequencing was used for molecular antigen typing.

The patient's blood group type was 0 ccD.Ee, K positive. Antibody screening was weakly positive with all test cells in the IAT and negative in saline and with ficin-treated cells. Autocontrol and DAT with anti-IgG were both 3+ positive, while anti-C3d was negative. Eluate was 3+ reactive with all untreated panel cells in the IAT, but negative with papain-treated cells. There was no inhibition of the antibody using rBGAs of the specificities Ch, Rg, Kn^a, and Yt^a; however, complete neutralization was achieved with Sc1 rBGA in plasma and eluate. Sequencing of the SC-gene revealed SC*01 without polymorphisms, thus encoding for all high-prevalence Scianna antigens (SC1, -3, -5, -6, -7, -8, and -9), which are all expressed on the Sc rBGA.

Differential diagnosis of cases with a broad reactivity in the IAT and a positive DAT includes autoantibodies, multiple alloantibodies and antibodies to high-prevalence antigens in the context of a serologic transfusion reaction. This case report demonstrates that a reaction pattern, which is suspicious of warm-reactive autoantibodies but shows unusual results such as non-reactivity with enzyme-treated test cells, should cause additional antibody workup for determination of antibody specificity.

AS is a member of the scientific advisory board of Imusyn (manufacturer of the RBGAs). All other authors: None