Quantitative fluorescence cytometry

The phenotypes useful in distinguishing normal and neoplastic leukocytes are often identified by fluorescence staining reactions detected on flow cytometers. These reactions were originally observed by fluorescence microscopy, and cells were classified by human observers as simply negative or positive, with the positive cells sometimes distinguished as dim or bright. These terms are still used in analyzing flow cytometry (FCM) results. However, recent advances in our understanding of fluorescence signals from stained cells (1) now permit the translation of terms like "dim" and "bright" into real mass units of fluorescence intensity, a process that we call quantitative fluorescence cytometry (QFCM). Although the translation is not yet exact and certain technical details remain to be resolved, a general understanding of QFCM is now accessible and helpful in interpreting staining patterns.