Comparison of Diagnostic Methods and the Changes of IgG Subclasses in Children with Mycoplasma pneumoniae pneumonia

Youn, You Sook; Lee, Kyung Yil; Hwang, Ja Young; Yim, Jung Woo; Kang, Jin Han; Lee, Joon Sung

Abstract

PURPOSE
This study aimed to investigate the positive rate of 3 serologic methods and polymerase chain reaction (PCR) and the changes of IgG and IgG subclasses in children with Mycoplasma pneumoniae pneumonia (MP).
METHODS
Fifty children with pneumonia admitted to Daejeon St. Mary's Hospital, Korea, during MP outbreaks were evaluated for the diagnostic antibody status using 3 serologic methods: indirect micro-particle agglutinin assay (MAA, Serodia-Myco II, Fujirebio, Tokyo, Japan), cold agglutinins and enzyme-linked immunoassay (EIA, Platelia M. pneumoniae IgM & IgG BIO-RAD, Marnes-la-Coquette, France) and PCR. The levels of antibody for MP in each method were measured 2 times during hospitalization: at presentation and at discharge (mean interval, 6.5 days). The levels of IgG and IgG subclasses (IgG1, IgG2, IgG3 and IgG4) were also analyzed 2 times (at presentation and at discharge) using stored sera.
RESULTS
At presentation, the positive rates of the diagnostic methods were 52%, 38%, 30% and 12% for MAA, cold agglutinins, EIA and PCR assay, respectively. Following analysis of the repetitive measurement of the antibody, the positive rates of the diagnostic methods were 76%, 60% and 56% for MAA, cold agglutinins and EIA, respectively. The mean IgG level of MP patients increased during hospitalization (973+/-184 vs. 1,040+/-205 mg/dL; P=0.008). Among the IgG subclasses, the levels of IgG1 and IgG3 showed a significant increase during hospitalization (553+/-129 vs. 611+/-151 mg/dL, P=0.003 for IgG1; 43+/-27 vs. 47+/-30 mg/dL, P=0.005 for IgG3).
CONCLUSION
For the accurate and relatively rapid diagnosis of MP, a paired sample examination is mandatory, especially within a short-time period. The sensitivity of serologic tests for the diagnosis of MP may differ among commercially available kits. IgG1 and IgG3 appear to be the main IgG subclasses that show an increase after MP infection.