Extension of useful reagent shelf life beyond manufacturers' recommendations. Cell Markers Committee of the College of American Pathologists.

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were asked to save aliquots of primary antibodies during mid-1997 so that by spring 1998 the reagents would be "outdated" according to manufacturers' recommendations. Three tumors were immunostained both in mid-1997 and early 1998 (using outdated reagents in 1998).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.