Procedure:
Chinese children under 18 years of age with neutropenia ≤ 1.5 x 109/L lasting 6 months or more in our single center were recruited into the study between 2016 to 2018. Patients with secondary causes of neutropenia were excluded. Blood for anti-neutrophil antibody and genotyping was taken once at the time of recruitment and subsequently when neutropenia recovered to ≥ 1.5 x 109/L. A combination of two in-house methods including GIFT, GAT and commercial kit LABScreenTM multipanel were used for the detection of antibodies. The age of onset, age of recovery, duration of neutropenia, gender, serial neutrophil counts, incidence of invasive infection, use of G-CSF were examined.