EuroFlow-based and conventional FC gating strategies yield different Sézary cell levels. Bland-Altman’s plots reveal the differences between Sézary cell percentages (of total CD4⁺ T cells) as calculated using conventional gating strategies (A; CD4⁺CD26⁻ or B, CD4⁺CD7⁻) and EuroFlow approach (calculated percentages herein were based on the 8-color T-CLPD antibody panel). The difference (y-axis) between both methods is drawn against the average measures of both methods (x axis). The limits of agreement (dashed lines: mean difference ± 1.96 SD) are displayed. A y-value closer to 0 indicates a higher level of agreement. Compared with the CD4⁺CD26⁻ approach, the calculated bias was −0.78, with a 16.9 standard deviation and 95% limits of agreement from −33.9 to 32.4. These differences decreased at higher tumor burden levels. Compared with the CD4⁺CD7⁻ conventional method, Bland-Altman’s analysis calculated a considerable bias (−24.6) with 34.7 standard deviation and 95% limits of agreement from −92.6 to 43.4. Linear regression plots revealed an overall moderate (C) to poor (D) correlation between conventional and EuroFlow-based gating methods for assessing tumor burden in PB. Given are the slope plus standard error and r², and the significance level is indicated.