Assessment of interlaboratory variability in analytical cytology. Results of the College of American Pathologists Flow Cytometry Study.

In 1986, the College of American Pathologists introduced an interlaboratory proficiency testing program for clinical laboratories that perform flow cytometry. Specimens consisting of fresh human lymphocytes isolated from blood or tissue or neoplastic cells grown in culture were mailed to participants by overnight mail. Results of analyses for cell surface antigens on lymphocytes and for cellular DNA content were reported to the College of American Pathologists Computer Center and the summary data were mailed to participants. The results obtained to date indicate no reagent- or instrument-related biases for measurements of cell surface antigens or for cellular DNA content. Interlaboratory variability in enumerating lymphocytes of a given subset varies inversely with the percentage of such cells in each specimen. In our experience, it is feasible and practical to conduct an interlaboratory proficiency survey in clinical flow cytometry.