In Vivo micronucleus assay: Increased efficiency with an automated imaging system

The in vivo erythrocyte micronucleus (MN) test is a standard assay for detecting chromosomal damage; however, conventional manual scoring is labor-intensive and subject to inter-scorer variability. Although automated image-based scoring offers a practical alternative, its application to bone marrow analysis requires effective enrichment of erythrocytes, to reduce interference from non-target nucleated cells. We have established and validated an automated bone marrow MN scoring workflow, using the Metafer slide-scanning system and associated software platform. We have compared a conventional cellulose column-based enrichment method with a syringe-filter-based method. The filter method reduced residual non-erythroid cellular components more effectively than the column method, although both methods yielded preparations suitable for automated analysis. Automated scoring showed no significant differences from manual microscopy in MN frequency or polychromatic erythrocyte ratio, in either negative- or positive-control groups. Repeated analysis of the same slide demonstrated high repeatability. Automated and manual MN frequencies showed positive linear correlations in both column- and filter-enriched preparations, and Bland-Altman analysis showed overall agreement between the two scoring methods. Automated historical control data (HCD) generated from male and female rats and mice were comparable to manually established laboratory HCD. These findings demonstrate that automated image-based scoring combined with appropriate erythrocyte enrichment is a reliable and practical alternative to conventional manual scoring in the in vivo bone marrow MN assay and may improve analytical efficiency, objectivity, and reproducibility in genotoxicity testing.