Given the serologic reactions Anti-D 0, Anti-C 3+, Anti-E 3+, Anti-c 0, Anti-e 0, which genotype is most probable?

Given the serologic reactions Anti-D 0, Anti-C 3+, Anti-E 3+, Anti-c 0, Anti-e 0, which genotype is most probable?

• A. CDE/cde
• B. DCE/dce
• C. dCE/dCE
• D. Cde/cde

Answer: (C)

This pattern comes from how Rh antigens are arranged on two chromosomes (the diplotype) and how each chromosome’s RHCE gene determines which C/c and E/e antigens are present. If a red cell shows no D antigen (D negative) but has C and E antigens, and it does not display c or e antigens, the two chromosomes must both carry the CE combination without D. The only diplotype that fits is dCE/dCE: both chromosomes lack D (d) but carry C and E (CE), so the cells express C and E, but not c or e. That explains why anti-D yields no reaction, anti-C and anti-E yield strong reactions, and anti-c and anti-e yield no reaction. Other haplotypes would introduce D, or bring in c or e antigens, which would change the serologic reaction pattern and not match the observed results.

This pattern comes from how Rh antigens are arranged on two chromosomes (the diplotype) and how each chromosome’s RHCE gene determines which C/c and E/e antigens are present. If a red cell shows no D antigen (D negative) but has C and E antigens, and it does not display c or e antigens, the two chromosomes must both carry the CE combination without D.

The only diplotype that fits is dCE/dCE: both chromosomes lack D (d) but carry C and E (CE), so the cells express C and E, but not c or e. That explains why anti-D yields no reaction, anti-C and anti-E yield strong reactions, and anti-c and anti-e yield no reaction.

Other haplotypes would introduce D, or bring in c or e antigens, which would change the serologic reaction pattern and not match the observed results.