SOURCES OF VARIABILITY IN THE DETERMINATION OF MICRONUCLEI IN IRRADIATED PERIPHERAL-BLOOD LYMPHOCYTES

Following a dose of 4 Gy 250 kVp X-rays to the blood lymphocytes from three healthy donors the frequency of micronuclei was enumerated by th ree scorers. Eight slides were prepared from each blood sample with 10 00 cytokinesis-blocked binucleate cells being scored for micronuclei a nd a recount undertaken 3 weeks later. Seven possible sources of varia tion were investigated: differences between donors, scorers, the four stages of sample preparation and time. A complete factorial analysis i ndicated that the major sources of variation were differences between donors and differences between scorers. One scorer identified fewer mi cronuclei than did the other two scorers in all slides of the irradiat ed blood samples and gave wide and inconsistent results for baseline c ounts. These results suggest that the performance of scorers should be screened before undertaking analysis of micronuclei. The most strikin g result, however, was the consistent performance of the scorers on th e repeat counts compared with the very large differences between the s corers.