Spot counting to locate fetal cells in maternal blood and tissue: a comparison of manual and automated microscopy

BACKGROUND: Fetal cell detection in maternal tissue requires an accurate, efficient, and reproducible microscopy method. Our objective was to compare manual scoring to a commercially available automated scanning system for the detection of chromosome signals by fluorescence in situ hybridization (FISH). METHODS: X and Y chromosome FISH signals were detected on slides of calibrated mixtures of blood, paraffin-embedded liver sections, and post-termination blood. For manual scoring (400x magnification), the number of cells located and duration of scoring were recorded. For automated scanning using the Metasystems Metafer3/Metafer4 Scanning System (200x magnification), duration of scanning, number of gallery images generated, duration of manual review of gallery images, and number of confirmed fetal cells were recorded. RESULTS: From all slides the number of target fetal cells located by manual and automated microscopy was highly correlated (r = 0.90). However, automated scanning required on average 4-fold more time than manual scoring (P < 0.0001), with an average automated scanning time of 9.7 h per slide compared with 2.4 h per slide when scored manually. CONCLUSIONS: In general, the accuracy of automated and manual microscopy is comparable, although manual scoring is more efficient because of the level of magnification necessary for automated scanning of cells, and a large number of gallery images generated by automated scanning that must then be reviewed manually. This suggests that when rapid analysis is required (i.e., clinical situations), manual microscopy is preferable. In contrast, automated scanning may have advantages over manual microscopy when time constraints are less imposed (i.e., research situations).