INSTRUMENT-DEPENDENT FLUOROCHROME SENSITIVITY IN FLOW CYTOMETRIC ANALYSES

Flow cytometry has become the preferred technique by which critical cl inical evaluations are made such as CD4 counts and aneuploid analyses. Mounting concern has arisen over the numerous techniques, reagents, a nd different flow cytometers employed to determine these data. Several studies have documented significant differences in results when diffe rent flow cytometers are utilized to analyze the same sample. Fluoroch rome-dependent instrument sensitivity also has been reported by numero us investigators. As more and more procedures are performed by cytomet ric analysis, light scatter and fluorescence limitations, which appear to be instrument dependent, demonstrate that not all flow cytometers have the same capabilities. Attempts were made to calculate molecules of equivalent soluble fluorochrome (MESF) values on nine different flo w cytometers using fluorescein isothiocyanate (FITC) and R-phycoerythr in (R-PE) labeled microsphere reference standards produced by Flow Cyt ometry Standards Corporation (FCSC). Dramatic differences were observe d in the ability of some cytometers to resolve these microspheres, The diminished resolution appeared to be instrument model and fluorochrom e dependent. We propose that diminished fluorescence resolution in cer tain flow cytometers could be responsible for significant variability in clinical values reported from laboratories utilizing different flow cytometers. (C) 1995 Wiley-Liss, Inc.