Detection of anti-neutrophil antibodies in autoimmune neutropenia of infancy: a multicenter study.

BACKGROUND Autoimmune neutropenia of infancy is caused by neutrophil-specific autoantibodies. Primary AIN is characterized by neutrophil count < 500 ml and a benign self-limiting course. Detecting specific antibodies against the polymorphic human neutrophil antigen usually confirms the diagnosis. Current available tests, however, are expensive and inapplicable in many laboratories as they require the use of isolated and fixed granulocytes obtained from donors pretyped for their distinct HNA alloform. OBJECTIVES To assess the performance of a modified test to identify by FACS-analysis granulocyte-specific antibodies in the sera of neutropenic children. METHODS We evaluated 120 children with a clinical suspicion of AIN, whose sera were analyzed by flow cytometry for the presence of autoantibodies using the indirect granulocyte immunofluorescence test. In contrast to the traditional tests, the sera were tested against randomly selected untyped neutrophils derived from a batch of 10 anonymous healthy subjects, presumably including the common HNA alloforms. Control sera samples were from patients with chemotherapy-induced, familial or congenital neutropenias. To further assure the quality of the new test, we retested six samples previously tested by the gold standard method. All medical files were screened and clinical outcomes were recorded. RESULTS Our method showed specificity of 85%, sensitivity of 62.5%, and a positive predictive value of 91.8%, values quite similar to those obtained by more traditional methods. CONCLUSIONS The new method showed high specificity for detection of anti-neutrophil antibodies in the appropriate clinical setting and could be an effective tool for clinical decision making.