Diagnostic value of cell bound and circulating neutrophil antibody detection in pediatric neutropenia

Background: Chronic benign neutropenia of infancy includes primary autoimmune neutropenia (pAIN) and chronic idiopathic neutropenia (CIN). A diagnosis of CIN is supported by the absence of free and/or cell-bound neutrophil autoantibodies, which can be detected by flow cytometry with the indirect-granulocyte immunofluorescence test (I-GIFT) and direct-granulocyte immunofluorescence test (D-GIFT), respectively. Conclusive evidence is lacking on the diagnostic value of the D-GIFT, whose performance requires specific laboratory expertise, may be logistically difficult, and hampered by very low neutrophil count in patient samples. This study investigated whether the evaluation of D-GIFT improves the diagnostic accuracy of pediatric neutropenia. Procedure: I-GIFT and D-GIFT were performed in 174 pAIN, 162 CIN, 81 secondary AIN, 51 postinfection neutropenic, and 65 nonautoimmune neutropenic children referred to this laboratory during 2002–2014. Results: Using 90% specific median fluorescence intensity cut-off values calculated by receiver operating characteristic curves, D-GIFT was positive in 49% of CIN patients, who showed similar clinical features as those with pAIN. In 44 (27%) of 162 CIN patients, I-GIFT was repeated two to three times in a year, resulting positive in 12 and two patients at second and third screening, respectively. Interestingly, 10 of the latter 14 patients showed a positive D-GIFT at the first serological screening. False positive D-GIFT was shown by 12% and 22% of nonneutropenic and nonautoimmune neutropenic patients, respectively. Conclusions: D-GIFT evaluation improves the diagnostic accuracy of pediatric neutropenia, but improvement of cell-bound antibody detection is needed to decrease false positive results.