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.