QUALITY-CONTROL STUDY OF THE ITALIAN GROUP OF CYTOMETRY ON FLOW-CYTOMETRY CELLULAR DNA CONTENT MEASUREMENTS

A quality control study on DNA flow cytometry, extended to 43 national laboratories, has been carried out by the Italian Group of Cytometry, using defined fixed suspensions of cultured human leukemia K562 cells and human blood lymphocytes. The participating laboratories were allo wed to follow their own staining and measurement protocols. Aliquots o f cellular suspension had to be measured three times on the same day a nd two other times on different days. A large heterogeneity of procedu res emerged among participants. The average of mean DNA index laborato ry values, from 36 laboratories who sent evaluable data, was 1.68, wit h a range from 1.49 to 1.97. The coefficients of variation ranged from 2.35 to 9.39% and from 2.79 to 8.5% for diploid and aneuploid peaks, respectively. Statistical analysis of the results showed quite good in tralaboratory reproducibility, but statistically significant differenc es were observed among laboratories, for both DNA indices and coeffici ents of variation. These differences appear to be consistent. For stan dardization, it is essential that efforts should be made to identify t he main sources of variation and to control them.