Flow cytometric detection of neutrophil-associated immunoglobulin in patients with or without neutropenia and establishment of the reference interval

We measured neutrophil-associated immunoglobulin (NAIg) levels using flow cytometry to establish the reference interval for NAIg and to estimate NAIg in patients with or without neutropenia. Peripheral blood from 152 individuals was analyzed for NAIg detection by flow cytometry. Using fluorescescent-conjugated anti-CD10 monoclonal antibody and anti-human immunoglobulins, proportions of NAIgG, NAIgA, and NAIgM bound to neutrophils were measured. Reference intervals for NAIg were set as NAIgG <2.6%, NAIgA <3.2%, and NAIgM <3.4%, representing the 95th percentile of data from 40 healthy individuals. 63 patients with neutropenia showed positivities of 49.2% (31/63) for NAIgG, 50.0% (19/38) for NAIgA, and 42.9% for (27/63) NAIgM. The proportion of NAIgA-bound neutrophils was higher in females (median 10.7% vs 3.0%, P=0.024), and NAIgA positivity rates were increased in patients aged less than 10 years (83.3%, P=0.043). NAIg was associated with the severity of neutropenia. In particular, NAIgM levels were significantly increased in patients with severe neutropenia (P=0.019). In addition, NAIg was commonly detected in patients with autoimmune diseases, solid organ tumors, hematologic disorders, and lymphoma. Flow cytometry permitted rapid detection of NAIg in small samples. Using this method, and using the reference intervals defined herein, patients with neutropenia or adverse transfusion reactions may be evaluated in a clinically relevant manner.