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| Variations in antibody strength The antibody in the pretransfusion specimen (prior to the patient being transfused with two units of unmatched group O Rh-negative RBC) reacted 2+ and 3+ with antibody screen and donor cells.If Jk(a+), the transfused donor RBC would have stimulated increased antibody production and the patient's plasma would be expected to react even more strongly with Jk(a+) red cells than in the pretransfusion specimen.However, the expected increase in antibody strength did not happen. Because Jk(a+) donor cells "mop up" (adsorb) the patient's anti-Jka, initially the anti-Jka decreased in strength. Later, once donor red blood cells are no longer present to adsorb the antibody, the anti-Jka would be expected to become stronger.Currently, (2-weeks post-transfusion) the patient's plasma is only reacting 1+ with Jk(a+b-) RBC and w+ with Jk(a+b+) RBC.This effect is called dosage. Learning points When a secondary immune response occurs, antibody first decreases before it increases. The expected increase in antibody strength will vary depending on the amount of excess antibody available in the patient's plasma at the time of testing versus the amount that had adsorbed to donor rbc and been removed by EVH.~ | View Page |
| DAT change of status Notice that the patient's DAT is now negative (IAT autocontrol in the panel done 2-weeks post-transfusion is negative). Cell Rh Rhesus Kell Duffy Kidd MNSs P Lewis Lu Results Cell C D E c e Cw K k Kpa Fya Fyb Jka Jkb M N S s P1 Lea Leb Lua Gel IAT* 1 rr 0 0 0 + + 0 0 + 0 + 0 + 0 0 + + + +S + 0 0 1+ 1 2 rr 0 0 0 + + 0 0 + 0 + 0 + + 0 + + + +S + 0 0 w+ 2 3 rr 0 0 0 + + 0 0 + 0 + + 0 + 0 + + 0 + 0 + 0 0 3 4 r"r 0 0 + + + 0 0 + 0 + + 0 + 0 + 0 + + + 0 0 0 4 5 R2R2 0 + + + 0 0 + 0 0 + + + + + 0 + 0 + 0 + 0 w+ 5 6 R2R2 0 + + + 0 0 + + 0 + + + + + 0 + 0 + 0 + 0 w+ 6 7 R1R1 + + 0 0 + 0 0 + 0 0 + 0 + + 0 + 0 +S 0 + + 0 7 8 R1R1 + + 0 0 + 0 0 + 0 0 + + 0 + 0 0 + + + 0 0 1+ 8 9 RZR1 + + + - + 0 + + 0 + 0 0 + + 0 0 + + + 0 0 0 9 10 r'r + 0 0 + + 0 0 + 0 + 0 0 + + 0 + 0 +S 0 + 0 0 10 11 Auto 0 11 The DAT is now negative because most or all of the transfused donor RBCs have likely been removed from circulation by the patient's anti-Jka.Red cells sensitized with IgG antibodies such as anti-Jka are trapped in the spleen by macrophages with receptors for the Fc part of IgG molecules. They may also be trapped by macrophages in the liver if they are coated with complement (C3) as well.Thus anti-Jka usually causes extravascular hemolysis (EVH). However, because anti-Jka binds complement, some intravascular hemolysis (IVH) may occur if the spleen is overwhelmed by IgG-sensitized red cells and red cells are left in the circulation long enough for them to hemolyze due to C9 binding. | View Page |
| Antigen phenotyping A standard follow-up to antibody identification is to antigen phenotype: Patient's red cells (expecting them to lack the corresponding antigen) Donor red cells (in this case, those transfused before an antibody was identified, or, more typically, to find suitable antigen-negative donors to crossmatch prior to transfusion).If you had wanted to type the patient for any antigens at this point in the investigation (2-weeks post-transfusion), which specimen would you have used? Think about any antigen typing problems and how to overcome them before proceeding to the next page. | View Page |
