Role of Additional Erythrocyte and Reticulocyte Parameters Offered by Sysmex XN ‐9000 in the Diagnostic Workup of Hereditary Spherocytosis: A New Screening Algorithm According to Age

Introduction Numerous algorithms based on recent developments of additional parameters on last generation haematology analysers have opened new perspectives for hereditary spherocytosis (HS) screening. Although some studies have demonstrated significant age‐related variation for reticulocyte‐derived parameters, these algorithms did not consider patients' age. Moreover, the apparent lack of short‐term stability of some parameters could represent an obstacle to their use if not performed as first‐line testing. This study aimed to identify robust and discriminating parameters that could be used for HS screening at any patients' age. Methods After an evaluation of the reference values and stability of the additional parameters offered by the Sysmex XN‐9000, we retrospectively collected and analysed the haematological parameters of 103 confirmed HS patients and 124 controls. The HS group was also compared to 116 samples from patients affected with other red blood cell or iron disorders. Results Our findings confirm that the reticulocyte count (Ret) and its ratio to the immature reticulocyte fraction (Ret/IRF) are the most effective and robust parameters for HS screening, with stability up to 48 and 96 h at room temperature (RT) and 4°C, respectively. The Ret/IRF ratio was mostly affected by patients' age rather than haemoglobin levels. We therefore proposed different algorithms that can be adapted to the laboratory's needs and that incorporate age‐specific thresholds for Ret/IRF. The combination of Ret and Ret/IRF allowed a sensitivity between 91.3% and 100% and a specificity between 77.1% and 94.2%. Conclusions This new age‐dependent algorithm using Sysmex's most stable parameters offers an easy‐to‐use tool for HS screening, even in cases of delayed or residual blood analysis.