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A multicenter study evaluating three methods for counting residual WBCs in WBC-reduced blood components: Nageotte
1Blood Transfusion Service, Massachusetts General Hospital, Boston, MA 02114, USA. sdzik@partners.org
Background:
A multicenter study was conducted to evaluate the performance characteristics of flow cytometry and microfluorimetry for counting low concentrations of WBCs and to compare the results with Nageotte hemocytometry.
Study Design And Methods:
A two-phase study involving 10 centers located in the United States and in Europe was performed. Coded samples of RBCs and platelets were distributed by 24-hour (Phase 1) or 2-day (Phase 2) courier service to each test site for analysis. Samples were prepared to include concentrations of WBCs slightly above and below the concentration corresponding to the threshold standards for WBC-reduced RBCs and platelets. All centers tested samples by Nageotte hemocytometry plus one or both of two automated methods.
Results:
Both flow cytometry and microfluorometry gave better results than Nageotte hemocytometry in testing freshly prepared samples. At WBC concentrations >5 per microL (RBCs) or >3 per microL (platelets), the intersite CV was <20 percent for the automated methods but >30 percent for the Nageotte hemocytometer method (p<0.001). Accuracy was greater for the automated methods than for the Nageotte hemocytometer method (p<0. 001). Nageotte hemocytometry showed a bias to underestimation relative to the results obtained with the automated methods. All methods had poorer performance in testing samples that required > or =2 days' shipment than in testing of those requiring overnight shipment.
Conclusion:
Automated methods for counting residual donor WBCs in WBC-reduced cellular components offer advantages of improved precision and greater accuracy than are seen with the Nageotte hemocytometer method. Automated methods are less labor-intensive but more costly than microscopic methods. Preparation and shipping methods will need further refinement for samples to be counted more than 24 hours after sample collection.