We run a separate control for each histochemical stain performed; the control slides are filed with the case.  With regard to immunoperoxidase staining, we run one positive control for each antibody (regardless of the number ordered).  The positive control is dated, as is the negative control(s) for the case.  The positive control slides are filed separately according to date.  When we have to review an old case, we identify the date on the negative control slide and then pull the positive control slides from that date.

R. Cartun