The diagnostic accuracy of Sysmex XN for identification of pseudothrombocytopenia using various thresholds for definition of platelet aggregation

Abstract

Introduction: The aim of this study was to investigate the diagnostic accuracy of the flag PLT-Clumps from the WNR/WDF and the PLT-F channels from Sysmex XN and to study how different cut-offs for investigation for pseudothrombocytopenia (PTCP) and the definition of platelet aggregation affected the diagnostic accuracy.

Methods: A smear review was performed for samples with platelet count <150 × 10⁹ /L and samples flagged for platelet aggregation by Sysmex XN-20. The samples were investigated for platelet aggregation in 30 fields using 40× objective. Findings were classified by size and quantity using two definitions of aggregation: the Norwegian quality improvement of laboratory investigations (Noklus) and the Groupe Francophone de'Hematologie Cellulaire (GFHC). The Q-values for the PLT-Clumps flag from the WNR/WFD channel and the PLT-F channel were compared with smear findings.

Results: ROC analysis showed that the diagnostic accuracy of the PLT-clumps flags increased with increasing stringency of the definition of platelet aggregation and when only samples with thrombocytopenia were investigated. With the most stringent PTCP definitions, the diagnostic accuracy of the PLT-Clumps flag from PLT-F was very high (AUC 0.97-0.98) and markedly better than for WNR/WDF.

Conclusion: The diagnostic accuracy of PLT-F from Sysmex XN-20 for identification of PTCP was very good and superior to the WNDR/WDF channel in samples with platelet count <150 × 10⁹ /L and a moderate to high number of aggregates in the smear. There is a need for a more precise definition of platelet aggregation.

Keywords: Sysmex; hematology instrument flag; platelet aggregation; platelets; pseudothrombocytopenia.

FIGURE 1

(A) Inclusion of samples. (B) Graphic presentation of 30 fields in a smear investigated for platelet aggregation. Created in BioRender

FIGURE 2

Percentage difference between platelet count in Na‐Citrate and EDTA‐blood as a function of the observed number of aggregates in 30 fields with a 40× objective (n = 44)