Neutrophils are part of the granulocyte family and play an important role in innate immunity. Neutrophils or polymorphonuclear neutrophils (PMNs) make up the largest proportion of circulating leukocytes. Patients with low PMN counts (neutropenia) or functional defects in PMN are more likely to be overwhelmed by infection. Granulocyte-reactive antibodies have been shown to play a key role in the pathophysiology of several immune-mediated neutropenias, transfusion-related acute lung injury (TRALI), auto-immune neutropenia after bone marrow transplantation and febrile transfusion reactions. Post-transfusion, in TRALI, the donor-derived antibodies can cause inappropriate activation of neutrophils leading to damage of the pulmonary microvasculature with severe clinical consequences. Thus, these disorders demand rapid and precise diagnosis using reliable neutrophil serology.