Evaluation of a rapid IgM antibody detection kit for diagnosis of Mycoplasma pneumoniae infection during childhood

Abstract

We evaluated the utility of a rapid detection kit for Mycoplasma pneumoniae (Mp)-specific IgM antibody, ImmunoCard (IC) Mycoplasma Test (Meridian Bioscience, USA), with regard to mycoplasmal infection during childhood. For this purpose, 30 serum samples were obtained from 23 pediatric patients with serologically proved mycoplasmal pneumonia at and younger than 16 years of age. The diagnosis of mycoplasmal infection was made by means of a particle agglutination (PA) method, which was on the basis of 1) a four fold or greater rise with paired sera or 2) at and more than 1:640 with a single, acute phase serum. In addition to the IC test, Mp-specific IgM and IgG antibodies were measured by ELISA tests (Zeus, USA) for comparison. A final observation time for colorization in the IC test was prolonged to 10 min in this study. The reason for this was because only 8 samples which were obtained 5 days or more after the onset of fever (37.5 degrees C) were judged to be positive when the observation time was confined to 5 min as the manufacturer recommended. A judgment was always made by more than one persons. Since we intended to find out the diagnostic capability of the IC test using an acute phase single serum, we focused on 18 cases for which samples were obtained within 5 days of the onset of fever. As a result, 13 (72%) cases were judged to be positive for Mp by the IgM ELISA test, 6 (33%) cases, including 5 cases in which the result was interpreted to be positive by a 10-min observation, were judged to be positive by the IC test, and 4 (22%) cases were judged to be positive by the PA test when titers of at and more than 1:320 by an acute phase single serum were interpreted as significant. Through this study we felt that the sensitivity of the IC test was not so high as have been previously reported in the literatures (the IC test was occasionally positive even in the range of < 1:40 by a PA test). On the other hand, we believe that the 10-min observation for final colorization did not significantly affect the specificity of the IC test as long as it was compared with the results by the ELISA IgM test. So far, the rapidity in obtaining results, and the simplicity of handling by which the test can be performed in an outpatient clinic, are thought to be the major advantages of the IC test.