Antibody expiration in the context of resource limitation: what is the evidence basis?

The implementation and enforcement of the College of American Pathologists Survey Checklist ANP 22432 has renewed attention on the issue of outdating of antibodies used for immunohistochemical analysis. The current study examined the staining patterns of 26 recently acquired primary antibodies and their expired counterparts. Two reviewers examined sequential sections of formalin-fixed, paraffin-embedded tissue samples for staining intensity and percentage of positivity. Appropriate positive and negative control studies were performed. Of the 26 antibodies, 20 exhibited no difference in percentage of positivity or staining intensity. Of the remaining 6, 3 showed better performance with the expired cohort and 3 with nonexpired antibodies. However, no antibody staining characteristics varied by more than 1 step, and in no case was positive staining lost after antibody expiration. Negligible differences exist in immunostaining between outdated and current antibodies. Thus, exemption for primary antibodies from existing regulations would conserve resources without adversely impacting patient care.