Abstract. Karlström R, Gustafson R, Palmblad J (The Karolinska Institutet at Huddinge University Hospital, Stockholm, Sweden). Chronic mild neutropenia in adults: relation to IgG3 deficiency and infection susceptibility. J Intern Med 2001; 250: 342–347.

Objectives. Chronic mild neutropenias (NP, i.e. absolute neutrophil blood counts/ANC/0.5–1.5 × 10⁹ L⁻¹) are accompanied by a variable infection susceptibility, which may or may not be as a result of concomitant conditions. Here, we assessed whether such patients also displayed an immunoglobulin deficiency and if this condition contributed to infection proneness.

Design, setting and subjects. Thirty consecutive adult Caucasian patients with chronic mild NP were followed at one university hospital for up to 28 years. Comparisons were made with 49 IgG3 deficiency patients at an immunodeficiency clinic.

Main outcome measures. Recorded infections, ANC and serum immunoglobulin levels; flow cytometry assessments of blood lymphocyte subsets and tests for autoimmunity were run to determine neutropenia subtypes. Results. Forty per cent of the NP patients were treated for severe or recurrent infections. The mean IgG3 value for the NP patients was significantly lower than for healthy controls (P < 0.005) and 33% of the patients displayed IgG3 values below the reference values (i.e. below 0.21 g L⁻¹), and an additional 13% had IgG3 values within the range others consider low (0.21–0.41 g L⁻¹). Unexpectedly, neutropenic IgG3 deficiency patients exhibited less infection proneness than those with normal IgG3 values (P=0.03). Patients with autoimmune, large granular lymphocyte‐associated or idiopathic NP had IgG3 deficiency in 63, 44 and 38%, respectively. In addition, none of IgG3 deficiency patients followed at the immunodeficiency clinic displayed neutropenia.

Conclusion. IgG3 deficiency is common amongst chronic mild neutropenia patients, particularly in those with autoimmune background, but contributes not significantly to infection susceptibility.