The antibody in the pretransfusion specimen (before the patient was transfused with unmatched group O Rh-negative RBCs) reacted 2+ and 3+ with the antibody screen and donor cells.
If Jk(a+), the transfused donor red blood cells would have stimulated increased antibody production. 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 "mopped up" (adsorbed) 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-) red blood cells and w+ with Jk(a+b+) red blood cells. This effect is called dosage.
Learning points:- When a secondary immune response occurs, the 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 red cells and been removed by extravascular hemolysis.
