QUALITY-CONTROL STUDY OF THE TOMETRY-ON-FLOW-CYTOMETRY-DNA-CONTENT-MEASUREMENTS .2. FACTORS AFFECTING INTERLABORATORY AND INTRALABORATORY VARIABILITY

A multicentric national quality control study has been organized under the auspices of the Italian Group of Cytometry to find a possible inf luence of some procedural steps in DNA flow cytometry measurements on DNA index (DI) values and to identify the main parameters affecting th e interlaboratory variability. To 40 participating laboratories we pro vided suspensions containing unknown mixtures of different cell types: an homogeneous thymocyte population used to check instrument linearit y; one mixture composed of two cell types characterized by DI = 1.00 a nd 1.10; and another composed of three different cell types with relat ive DIs of 1.00, 1.26, and 1.62, respectively. Possible effects due to staining protocols were studied, allowing the participants to stain c ellular DNA according to the procedure routinely adopted in each labor atory, in addition to a standardized procedure with a fixed PI solutio n. As far as the influence of instrument linearity on DI values is con cerned, we did not find any correlation with the DI variability observ ed, even if the use of a standardized staining protocol could lead to a sensible gain in interlaboratory DI reproducibility. Twenty-five of 40 (65%) laboratories were able to discriminate the near-diploid subpo pulation, and a coefficient of variation of less than 4% was the minim um condition necessary to recognize the DI = 1.1 population. In sample s containing two aneuploid subpopulations, 25 of 35 (71.4%) laboratori es showed a high reproducibility with the standard staining protocol a nd 22 of 38 (57.9%) with the free staining protocol. However, a sensib le improvement in interlaboratory reproducibility emerged with respect to the previous trial (Tirindelli Danesi et al.: Cytometry 14:576-583 , 1993). (C) 1997 Wiley-Liss, Inc.