A-153 Study of the evaluation of fragment flag and percentage schistocyte count in MINDRAY® BC-6800 PLUS in a public pediatric hospital in Argentina
Authors: Marcone I , Ottobre M , Colitto L 
Published: October 2024

Abstract

Background
Schistocytes are fragmented red blood cells (FRCs) that arise from the mechanical destruction of red blood cells (RBCs). They indicate the possible presence of a thrombotic microangiopathy (TMA). TMA includes hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura(TTP). ICSH defined schistocytes as 4 well stablish shapes always smaller than intact RBCs. The gold standard for the identification of schistocytes is microscopic evaluation. A schistocyte count should be considered clinically meaningful if it represent the main morphological RBCs abnormality in the periferic blood smear (PBS). The results should be expressed as a percentage, after counting at least 1000 RBCs in optimal areas of the PBS. The cut off for TMA was previously stablished in above 1% (adult population) and a higher percentaje in pre term newborns (above 5%). Some blood cell count analyzers have a flag for FRC, and some of them also provide methods for an automated FRC count, through the measurement of forward scatter and the intensity of fluorescence or 2-dimensional optical analysis. The Mindray® BC 6800 PLUS provides a flag for fragments and the research FRC% parameter that quantifies fragmented RBCs. When the flag and the FRC% are combined, can bring value to diagnostic TMA.

Objetives
Evaluate the sensitivity and specificity of the fragment flag to predict schistocyte on the PBS of pediatric samples. Evaluate the utility of FRC% as TMA diagnostic tool and compare with the gold standard.

Methods
725 pediatric samples were analyzed (0-18 years).16 of them was patient samples diagnosed with TMA. All blood cell counts were determined using Mindray®BC-6800 PLUS. Cut off 1% was considered for FRC% in TMA. Inclusion criteria for TMA samples include thrombocytopenia, increased lactate dehydrogenase and decreased hemoglobin concentration. Schistocyte counting was carried out from May-Grunwald-Giemsa-stained PBS according to the recommendations proposed by ICSH. Only ICSH established shapes were kept as valid.

Results
Regarding the sensitivity of the fragment flag, it was 84.62% with a specificity of 91.13% to detect the presence of schistocytes in PBS samples. In the Bland-Altman analysis, the FRC% shows a difference with a tendency to underestimation with respect to the observation on the PBS, which was less at lower percentages of schistocytes. The sensitivity of the FRC% to TMA was 75% while the specificity was 94.36% and a negative predictive value (NPV) of 99.41%.

Conclusions
Fragments flag represents a potentially powerful tool for screening of squistocytes in pediatric samples. Although sensibility and NPV for FRC% authomatical counts were acceptable, a few false-negative samples were found. Presence of FRC% below a threshold of 1% could exclude TMA.However PBS microscopic observation is still the gold standard to determine squistocytes presence. For the purpose of complete our study and to get further larger scale prospective data, we started collecting all data for all samples entering the laboratory in order to improve an authomatical method that should have a more rapid turn-around time at lower costs.