Reference Range for the Automated Fragmented Red Cell Parameter and Its Diagnostic Utility in Red Blood Cell (RBC) Fragment Quantification: A Prospective Study.

Background The automated measurement of fragmented red blood cells (FRCs) is a recently introduced parameter available on modern hematology analyzers, including the XN-Series™ Automated Hematology Analyzers (Sysmex Corporation, Kobe, Japan). Its clinical relevance lies in its potential to correlate with schistocyte counts, which is a critical diagnostic step in thrombotic microangiopathies and related disorders, as their presence reflects microangiopathic red cell fragmentation and guides urgent clinical decision-making. Schistocyte quantifications are traditionally assessed manually on stained peripheral blood smears using light microscopy. However, the accuracy of FRC measurement is highly dependent on the specific technology and methodology employed by each analyzer, making the establishment of instrument-specific reference ranges essential. This study aimed to establish a reference range for FRC and to evaluate the correlation between manual schistocyte counts and automated FRC measurements. Methods We analyzed 179 normal samples from voluntary blood donors using the XN-Series™ automated hematology analyzer to establish the reference range for FRC. In addition, we evaluated the influence of other red blood cell (RBC) parameters on FRC measurements. To assess the diagnostic performance of FRC, we further analyzed 100 patient samples by comparing the automated FRC values with manual schistocyte counts performed on stained peripheral blood smears, using Bland-Altman analysis for agreement assessment. Results Based on the analysis of 179 healthy samples, the reference interval for the absolute FRC count (FRC#) was 0.0 to 0.125/µL, and for the FRC percentage (FRC%), it was 0.0 to 0.00515%. Elevated Hypo-He (hypo hemoglobin equivalent) values (red cells with hemoglobin content <17 pg) were associated with spurious increases in FRC measurements, suggesting potential analytical interference. In a separate cohort of 100 patient samples, an FRC% threshold of <1% demonstrated a negative predictive value (NPV) of 70% for excluding the presence of schistocytes on peripheral blood smear. Bland-Altman analysis comparing manual schistocyte counts with automated FRC% revealed a mean bias of 0.287, with 95% limits of agreement ranging from -2.2 to 2.8, indicating moderate agreement between the two methods. Conclusion Establishing reference ranges for FRC not only enhances clinical interpretation but also provides valuable feedback to hematology analyzer manufacturers for refining automated smear-generation rules. As an initial screening tool, the FRC parameter could help safely exclude over two-thirds of samples (NPV = 70%) from manual review, reducing the burden of time-intensive schistocyte quantification. Such selective flagging has the potential to improve laboratory efficiency without compromising patient safety, enabling laboratory physicians to prioritize and triage cases more effectively. The upper reference limit was well below the ≥1% schistocyte threshold for thrombotic microangiopathic anemia (TMA), supporting the role of elevated FRC as a trigger for manual smear review, which remains indispensable whenever TMA is clinically suspected.