Selective Immunoglobulin M Deficiency Among Clozapine-Treated Patients: A Nested Case-Control Study



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Objective: To analyze the presence of selective immunoglobulin M immunodeficiency (SIgMD) among long-term clozapine-treated outpatients in a nested case-control study.

Method: We investigated 33 patients who took clozapine and found 6 patients with SIgMD. These patients were compared with 67 patients not taking clozapine, of whom 2 had SIgMD. Of these 6 and 2 patients, we made a group of 8 case-patients with SIgMD. This group was compared with 92 (27 + 65) patients without SIgMD matched to cases on age, sex, weight, mental health unit, diagnosis, and psychiatric medication. In both groups there were patients who had taken clozapine: 6 of 8 in the SIgMD group (75%) and 27 of 92 in the non–SIgMD group (29%). SIgMD was defined by mean IgM values ≤ 30 mg/dL. IgM measurements were performed every 6 months, and the data were averaged for each subject. The study was conducted from January 2009 to December 2013.

Results: We found a statistical association between clozapine use and the presence of SIgMD (OR = 7.2222; 95% CI, 1.3704–38.0623; Z = 2.332; P = .0197).

Conclusions: Due to the high incidence of SIgMD observed in schizophrenic patients treated with clozapine, clinicians should pay particular attention to not only granulocyte counts but also patterns of IgM decline to prevent drug iatrogenesis.

Prim Care Companion CNS Disord 2015;17(4):doi:10.4088/PCC.15m01782