ABO Incompatibility: Why Type B Blood Cannot Be Given to Type A Recipients

ABO mismatch causes acute hemolytic transfusion reaction (AHTR) due to preformed IgM antibodies.

Antigen-Antibody Pairs

• Type A RBCs have A antigen; plasma contains anti-B.
• Type B RBCs have B antigen; plasma contains anti-A.

If type B blood is transfused into a type A recipient, the recipient’s anti-B IgM binds donor B antigens → complement activation → intravascular hemolysis → hemoglobinemia, hemoglobinuria, DIC, renal failure, shock, death.

Prevention

• Type and screen (recipient) + crossmatch (donor unit vs. recipient serum).
• Electronic crossmatch if antibody screen negative.
• Two independent patient ID checks at bedside.

AHTR Presentation

• Fever, chills, flank pain, dark urine within minutes-hours.
• Labs: ↓Hb, ↑LDH, ↑bilirubin, ↓haptoglobin, +DAT, schistocytes.

Immediate stop transfusion, aggressive hydration, diuresis, monitor renal function. ABO compatibility is absolute; Rh and minor antigens managed separately.