All the slides were examined at ×600 magnification using a Nikon Optiphot 2 fluorescence microscope, equipped with separate filters for DAPI and fluorescein isothiocyanate (FITC). Manual scoring was timed for three unirradiated and three 1 Gy/1 h incubated samples on slides produced by both processing methods. A total of 50 lymphocytes were scored per sample and the time taken to do this was recorded every ten cells. To ensure the lyse/fix processing itself did not affect foci levels, samples irradiated at 0.5 Gy/repair time 30 min and prepared using both protocols were used to assess the number of foci per cell seen in a panel of 17 donors. 50 lymphocytes were scored in each of the reference samples and the foci numbers were used to adjust the calibration coefficients and the associated standard errors (Rothkamm et al., 2013b (link)) of the laboratory’s calibration curve (Horn, Barnard & Rothkamm, 2011 (link)). Blood dose estimates for the unknown samples were produced by scoring up to 50 lymphocytes or 200 foci per sample.