Can anyone give me any info on validating rare antisera (AHG) for use in gel? I would like to initiate this to try to save $$$.

You would do it in exactly the same way that you would validate any other antisera for use in gel.

The hard trick is getting hold of the rare negative red cells to use for the validation and as the negative control for future use. Of course, once the antisera are validated, IF you are using them for screening purposes only, then don't use a negative control until such time as you suspect you have a genuine negative. Then, of course, you would have to use proper controls throughout.