Serum Immunoglobulin G is a Marker for the Risk of Opportunistic Infection in Steroid-dependent Severe Asthmatic Patients

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Approximately 10% of asthmatic patients are refractory to inhaled corticosteroids and therefore need long-term oral corticosteroid therapy, which is associated with a risk of opportunistic infections due to immunosuppression. To ascertain the applicability of serum Immunoglobulin G (IgG) as a marker for predicting the risk of opportunistic infections in patients undergoing oral corticosteroid therapy. Three thousand asthmatics were screened, and 14 patients who had been administered daily oral corticosteroids for more than two years were enrolled. The patients enrolled were maintained under observation with ordinary check-ups and treatments for one year. After the observation period, the patients were divided into two groups according to the presence (OPI) or absence (non-OPI) of opportunistic infections during the period. The differences in the clinical parameters between the groups were investigated. There were no statistically significant differences in age, forced expiratory volume in 1 second (FEV(1)), smoking status or serum albumin between the groups. The serum IgG level of the OPI group was significantly lower than that of the non-OPI group (567.2±151.1 mg/dL vs. 931.6±198.8 mg/dL, p<0.01). The average total dose of corticosteroids administered during the one year period was higher in the OPI group (2,633±554.2 mg) than that in the Non-OPI group (1,793±466.2 mg) (p<0.05). There was a significant correlation between the serum IgG and total dose of corticosteroids administered during the one-year period (r = -0.75, p<0.01). The area under the receiver operating characteristic curve regarding the serum IgG and incidence of opportunistic infections was 0.97, which suggests that the serum IgG level has a high accuracy for predicting the risk of opportunistic infections. The serum IgG was therefore found to be a useful marker for predicting the risk of opportunistic infections in steroid-dependent asthmatics.