LAUSR

Hereditary spherocytosis (HS) is an inherited anaemia that results from deficiency of integral membrane proteins of erythrocytes. Affected red blood cells (RBCs) have unstable cytoskeleton. They lose their typical shape and change into spherocytes. These cells are more prone to haemolysis due to decreased area/volume ratio and damaged plasma membrane. Diagnosis of HS in neonates might be difficult, due to the physiological presence of spherocytes in the blood film of newborns and normal haemoglobin levels at birth.1 Moreover, in neonates, typical symptoms of HS, such as anaemia, splenomegaly and jaundice, rarely occur. Most of neonates with HS have parents, who are symptomatic but also who can be asymptomatic. But still, ~35% of HS cases are de novo mutations.2 A screening test for HS is the eosin‐5’‐maleimide (EMA) binding test—a flow cytometric analysis of fluorescent EMA dye binding to plasma membrane protein (mainly band 3 protein, which remains connected with spectrin, ankyrin and protein 4.2) on the surface of the erythrocyte. According to International Council for Standardization in Haematology (ICSH) and British Committee for Standards in Haematology (BCSH) guidelines, the result of the EMA binding test does not depend on the patient’s age and blood morphology; thus, it may be performed as a screening test in infancy. To properly perform and interpret an EMA binding test, 5‐6 control samples were stained and analysed parallel to the patient’s blood. It allows for the direct comparison of the fluorescence of patients’ EMA‐bound erythrocytes and normal EMA‐bound RBCs. According to literature data, HS affected RBCs are characterised by a decrease in EMA fluorescence beneath ~80% compared with control RBCs. The threshold for the diagnosis of HS should be established for each laboratory performing the test separately.3 It is more suitable to express EMA test results in percentage of fluorescence of control cells rather than mean fluorescence intensity, since different values of its intensity can be obtained using different flow cytometers or even samples of a dye prepared for staining. The cut‐off value for an EMA test to diagnose HS differs between laboratories and studied populations.4-11 Many studies do not include newborns to analyse EMA test specificity and sensitivity. If so, a limited number of patients are included.12 Thus, we decided to study EMA test usefulness in detection of HS in the first 9 weeks of life. 2 | MATERIAL S AND METHODS