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Objective: The College of American Pathologists Cell Markers Committee designed a study to evaluate the use of immunohistochemistry primary antibodies beyond manufacturers' recommended dates., Methods: Pathologists were asked to save aliquots of primary antibodies during mid-1997 so that by spring 1998 the reagents would be "outdated" according to manufacturers' recommendations. Three tumors were immunostained both in mid-1997 and early 1998 (using outdated reagents in 1998). Two hundred twenty-one laboratories participated., Patient Samples: Immunostained materials consisted of an angiomyolipoma immunostained for muscle-specific actin and HMB-45, a melanoma immunostained for S100 protein and HMB-45, and a large cell lymphoma immunostained for common leukocyte antigen and HMB-45. Blocks from the same tumor were used in each instance., Main Outcome Measure: We compared the immunostaining results as a percentage of laboratories indicating a positive or negative immunohistochemical result between the 1997 and 1998 time points., Results: Only minor differences were identified for the 221 reporting laboratories in 1998 as compared with those in 1997., Conclusions: The data suggest review of the Health Care Financing Administration's ruling on extending the useful reagent shelf life beyond manufacturers recommendations. Similar studies using more inherently quantitative methodology are suggested.

This review discusses several commonly used lineage-directed antibodies, including those to cytokeratins, vimentin, glial fibrillary acidic protein, neurofilaments, desmin, actin, leukocyte common antigen, and melanoma-specific antigen. Discussion is particularly directed to issues of antibody sensitivity and specificity, with several confusing and/or potentially beneficial examples of cross-lineage antigenic co-expression cited. The value of using limited panels composed of antibodies with complementary specificities is also emphasized.