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.


OBJECTIVE
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.
Sella
Ruti
R
Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
Flomenblit
Lena
L
Goldstein
Itamar
I
Kaplinsky
Chaim
C
D019268:Antibodies, Antineutrophil Cytoplasmic / Q000097:blood*; D001327:Autoimmune Diseases / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009503:Neutropenia / Q000276:immunology*; D009504:Neutrophils / Q000276:immunology; D012680:Sensitivity and Specificity
D019268:Antibodies, Antineutrophil Cytoplasmic