ClearLLab 10C reagents panel can be applied to analyze paucicellular samples by flow cytometry

The FDA-approved ClearLLab 10C Reagents Panel (Beckman Coulter) simplified the diagnosis of leukemias and lymphomas by flow cytometry. However, the requirement of using 3 × 10⁶ cells/mL cannot be met for paucicellular samples. Therefore, we tested whether this 10-color panel can be reliably employed to analyze specimens with low cell concentrations. Serial dilutions of 16 samples (5 normal, 11 abnormal), yielding concentrations ranging from 3.0 × 10⁶ to 0.0469 × 10⁶ cells/mL (64-fold difference), were stained using the B-cell and T-cell panels of the ClearLLab 10C system, and mean fluorescence intensity (MFI) was measured for each antibody. For each cell dilution, the deviation from the value obtained with the FDA-approved concentration of 3.0 × 10⁶ cells/mL was calculated. The agreement between the highest and lowest cell concentration data was evaluated by the Bland and Altman method, Pearson's and Spearman's correlation analyses, and linear regression. In all patients, the antigen expression pattern was similar at all cell concentrations tested, and the mean deviation of the MFI from the value obtained using 3.0 × 10⁶ cells/mL never exceeded 10% for any of the antibodies. The Bland-Altman method demonstrated the similarity between results obtained with the FDA-approved cell concentration and a 64-fold diluted cell suspension, and a high positive correlation was found between MFI acquired under these two conditions. The tests utilizing the lowest density of cells yielded the same patterns of antigen expression in all patients as those performed with the FDA-approved concentration, documenting a 100% concordance between these two protocols. The ClearLLab 10C panel can reliably determine the expression of markers of leukemias and lymphomas in paucicellular samples containing as little as 0.0469 × 10⁶ cells/mL (64-fold lower than the FDA-approved concentration). This finding markedly expands the applicability of the ClearLLab 10C platform in a clinical setting.