Special test methods include:
Serum antibody tests
Rapid ELISA test kits (96-well microtiter plate coated with antigen) are frequently used for detecting a qualitative immune response in serum to M. pneumoniae - IgM increases within one week of symptom onset - while IgG increases two weeks later. The problem with this test is the false-positive rate may be high, due to the body's ability to persist in providing an active immune response for up to a year after initial infection. (This makes identification of a current infection quite difficult.) In addition, false negatives may occur - some patients fail to produce detectable levels of IgM.
Popular rapid serological methods include the use of a membrane-based immunoassay (single card or single well format).
Indirect hemagglutination and metabolism inhibition tests are quite specialized and rarely used.
Antigen tests
Historically, antigen tests were abandoned in favor of PCR test methods. (See the page, "Recent Developments" for updated news.)
PCR
A type of Nucleic Acid Amplification test (or NAA) method uses polymerase chain reaction (PCR, especially real-time PCR) testing of nasopharyngeal specimens, as well as urethral/vaginal swabs. This method is useful as the PCR testing amplifies and detects the bacteria's genetic material. PCR test methods are quite specific. However, the cost may be prohibitive.
Several well-known rapid respiratory and genital PCR panel test platforms are now available for medical laboratory use. These screening tools typically include other pertinent bacterial and viral pathogens and the pathogenic Mollicutes in the multiplex test panel. For example, respiratory tract screening PCR assays may include M. pneumoniae, as well as many other pathogens such as Chlamydophila pneumoniae (Chlamydia) and Legionella pneumoniae. Some test methods have become quite rapid (1-hour turnaround time), allowing for opportunities to be used in point-of-care scenarios.
Limitations
- As with most laboratory testing, limitations may be present. One limitation is that positive test results must correlate with clinical findings. As many of these organisms are known to be commensal, a positive test may not have any meaning in the absence of clinical symptoms.
- It is possible to detect the organism by one test method and not another (eg, PCR positive/culture negative); recall that aside from detection issues caused by technical errors - PCR methods detect dead as well as live organisms. Also of note is the discrepant serological antibody test, which is dependent upon the (previously mentioned) patient's immune response.
Note: State public health laboratories may provide diagnostic support or even forward the patient specimen to the CDC for additional or confirmatory testing.
20. CDC/Gathany. Image #10026. "Centers for Disease Control and Prevention (CDC) Biologist, Damien Danavall, preparing what is known as a mastermix, that he would use in a multiplex real-time PCR assay." PHIL public domain. Created 2007. Accessed December 29, 2023. https://phil.cdc.gov/Details.aspx?pid=10026
