Background: A fully automated single-tube assay with tubes (BD TruCOUNT, BD Biosciences) for absolute counting of residual cells in freshly prepared plasma by flow cytometry was developed (BD Plasma Count).
Study design and methods: The nucleic acid dye thiazole orange stains white blood cells (WBCs). The monoclonal antibodies anti-CD41a-peridinin chlorophyll protein-Cy5.5 and anti-glycophorin A-fluorescein isothiocyanate label platelets (PLTs) and red blood cells (RBCs), respectively. No fixation, permeabilization, or washing steps were required. Validation was done according to guidelines of the International Conference on Harmonization and the National Committee for Clinical Laboratory Standards. Cell-free plasma was spiked with each cell type for accuracy, reproducibility, and linearity measurements.
Results: Results showed no carryover or drift under automated sample acquisition conditions. Nonspecific background was fewer than 0.3 cells per microL for residual WBCs (rWBCs), fewer than 2.7 cells per microL for rRBCs, and fewer than 85 cells per microL for rPLTs. Determinations of rWBC and rPLT counts were linear with a coefficient of variation of less than 12 percent for the imprecision. Owing to cross-linking of the anti-glycophorin A antibody, linearity and precision for rRBCs diverged up to 21 percent at a count of 6000 rRBCs per microL. In a 2-year period, five operators investigated 2666 quality control (QC) samples of fresh-frozen plasma on 108 working days. Maximum cell numbers found were 196 for rWBCs, 3960 for rRBCs, and 28,952 for rPLTs per microL. In 31 cases (1.2%) rWBCs were out of specification. No outlier was observed for rRBCs and rPLTs. Residual RBC cell numbers determined were always within the acceptable concentration range of the assay.
Conclusion: These data demonstrate that the single-tube test is suitable for routine QC assessment of the cellular contaminants of therapeutic plasma according to the European recommendations.