Comparison between Nageotte and flow cytometric counting of residual leucocytes in freshly prepared leucocyte-reduced red blood cell components

Abstract

Background Flow cytometry (FC) and Nageotte hemocytometry represent the most widely accepted methods for counting residual white blood cells (rWBCs) in leucocyte-reduced (LR) blood components. Our aim was to study the agreement between the two methods, under real working blood bank conditions. Materials and methods 94 freshly produced LR red blood cell (RBC) units were tested for rWBC concentrations by FC and Nageotte. To assess the precision of each method, we calculated the intra-assay coefficients of variation (CV), and followed the Bland-Altman methodology to study the agreement between the two methods. Results CV was 18.5% and 26.2% for the Nageotte and the FC, respectively. However, the agreement between the duplicate observations, using the binary cut-off threshold of 1 × 106 WBCs per unit to define the results as “pass/fail”, was 71.9% for the Nageotte and 93.3% for the FC. Linear regression analysis did not show any correlation (R-squared = 0.01, p = 0.35) between the two methods, while the Bland-Altman analysis for the measuring agreement showed a bias toward a higher Nageotte count of 0.77 × 106 leucocytes per unit (p < 0.001) with the 95% limits of agreement (d ± 2 sd) ranging from –0.40 × 106 to 1.94 × 106 leucocytes per unit. Conclusion The absence of agreement between Nageotte and FC method, with the differences within d ± 2 sd being of high clinical importance, suggests that the two methods cannot be used for clinical purposes interchangeably. The Nageotte seems unsuitable for quality control even with a pass-fail criterion, under real working blood bank conditions.