Comparison of MRD data obtained by 8-color EuroFlow FCM and routinely obtained molecular MRD data. Flow cytometric MRD data were compared with molecular MRD data and are shown for samples obtained at day 15 (A), day 33 (B), or day 78 (C). In the lower right part of each panel, the number of FCM⁻/PCR⁺, FCM⁺/PCR⁺, FCM⁺/PCR⁻, and FCM⁻/PCR⁻ is indicated. Only samples in which MRD could clearly be detected by FCM-MRD or samples which had sufficient cells acquired for reaching a sensitivity of ≤10⁻⁵ (ie, ≥ 4 × 10⁶ cells acquired) were included in the analyses. Based on a LOD of 10 events, the sensitivity of FCM-MRD was 2.5 × 10⁻⁶; the quantitative range (based on a LLOQ of 40 events) is 10⁻⁵. Consequently, FCM-MRD data between 2.5 × 10⁻⁶ and 10⁻⁵ should be considered positive, but are below the limit of quantitation.