Mixed-field agglutination

In transfusion medicine, mixed-field agglutination refers to mixed reactions during cell typing where two distinct cell populations are present: agglutinated cells admixed with many unagglutinated cells. The presence of two or more cell population is known as chimerism. Mixed-field agglutination is an important cause of ABO typing and genotype discrepancies. The cause of mixed field agglutinations should be sought prior to setting up blood for transfusion.^[1]

Causes

False chimerism

By far the most common cause of mixed-field agglutination is false chimerism artificially induced through transfusion of identical donor red cells or through a stem cell transplant.^[2][3] For example, a type B individual who has received massive transfusion of group O donor red cells may show mixed field agglutination with anti-B sera whereby his own group B red cells are agglutinated, while the group O donor red cells in his circulation are unagglutinated.

True chimerism

A true chimerism is a rare sporadic phenomenon whereby an individual has a dual cell population derived from more than one zygote. This may result from intrauterine exchange of erythrocyte precursors between twins (twin chimerism) or two fertilized eggs fuse into one individual. Twin chimerism results from mixing of blood between two twin fetuses through placental blood vessel anastomoses, leading to engraftment of hematopoietic stem cells from one twin within the marrow of the other. Each twin ends up with two distinct cell populations of varying proportions.

Reference

1. ^ http://faculty.matcmadison.edu/mljensen/BloodBank/lectures/ABO%20discrepancies.htm
2. ^ Roback, JD; Combs, MR; Grossman, BJ; Hillyer, CD. Technical Manual. AABB. 2008. pp353, 356.
3. ^ Bluth MH, Reid ME, Manny N. Chimerism in the immunohematology laboratory in the molecular bioplogy era. Transfus Med Rev 2007;21:134-46.