An example of anti-Yta demonstrating a change in its clinical significance.

The clinical significance of some red cell alloantibodies remains in doubt and can best be studied with long-term 51Cr survival studies. We report a patient whose IgG anti-Yta was initially shown not to shorten the lifespan of 51Cr-labeled Yt(a+) red cells. At the time of this study, the subclass of the antibody could not be determined. Twelve weeks after transfusion with 4 units of Yt(a+) red cells, the alloantibody for the first time was demonstrable as IgG1; a repeat radiolabeled red cell survival demonstrated significant shortening of the lifespan of Yt(a+) red cells when they were followed for 7 days. These cells had a marked 'two-component' survival curve. Because the patient also demonstrated autoantibody coating his red cells, the clinical effect of this autoantibody was followed with autologous red cells labeled with 111In; the survival of autologous red cells was normal throughout these studies. Evaluation of the clinical significance of an alloantibody in a patient may require long-term 51Cr red cell survival studies and repetition of these studies after exposure to large quantities of the antigen.