Extension of useful reagent shelf life beyond manufacturers' recommendations

Objective.-The College of American Pathologists Cell Markers Committee desi gned a study to evaluate the use of immunohistochemistry primary antibodies beyond manufacturers' recommended dates. Methods.-Pathologists were asked to save aliquots of primary antibodies dur ing mid-1997 so that by spring 1998 the reagents would be "outdated" accord ing to manufacturers' recommendations. Three tumors were immunostained both in mid-1997 and early 1998 (using outdated reagents in 1998).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 imm unostained for muscle-specific actin and HMB-45, a melanoma immunostained f or S100 protein and HMB-45, and a large cell lymphoma immunostained for com mon leukocyte antigen and HMB-45. Blocks from the same tumor were used in e ach instance. Main Outcome Measure.-We compared the immunostaining results as a percentag e of laboratories indicating a positive or negative immunohistochemical res ult between the 1997 and 1998 time points. Results.-Only minor differences were identified for the 221 reporting labor atories in 1998 as compared with those in 1997. Conclusions.-The data suggest review of the Health Care Financing Administr ation's ruling on extending the useful reagent shelf life beyond manufactur ers recommendations. Similar studies using more inherently quantitative met hodology are suggested.