Autoimmune neutropenia in children: Test cells versus beads and a role for pro-LL-37 and absolute neutrophil count.

Autoimmune neutropenia (AIN) in early childhood is caused by autoantibodies targeting neutrophil surface antigens, most commonly CD16 (FCGR3B), and must be distinguished from congenital neutropenia, malignancy-associated neutropenia and chronic idiopathic neutropenia (CIN). In this study, the diagnostic performance of the cell-based granulocyte agglutination test (GAT) and granulocyte immunofluorescence test (GIFT) was compared with the bead-based LabScreen Multi (LSM) assay in 214-suspected AIN cases. While 36% of samples were positive for anti-CD16 antibodies in GAT or GIFT, only 19% reacted against the same antigen in LSM, primarily against weak or Immunoglobulin M (IgM)-restricted antibody responses. Patients testing positive in all three assays exhibited significantly higher pro-LL-37 levels and lower absolute neutrophil counts (ANCs), indicating preserved granulopoiesis with peripheral destruction. Our findings question the use of LSM as a standalone test in AIN diagnostics. Incorporating pro-LL-37 and ANC in AIN diagnosis may improve differentiation between antibody-mediated neutropenia and other neutropenia forms in children.