How is a Chlamydia Screening Lab Test Done?
Isolation of Chlamydia in Cell Culture: this is 100%specific, but it has disadvantages, beinglaborious, expensive and relatively insensitive compared with newer test methods. Another problem is that clinical material has to be handled in a specific way e.g. time and storage conditions, for the test to be accurate.
Antigen Detection: The use of monoclonal antibodies makes the directdetection of chlamydia in clinical specimens possible. The target antigens that are are DFA and EIA. The sensitivityof DFA is 80–90% and the specificity is 98–99% compared to cellculture. 'Rapid tests' which do not require sophisticated equipment and canbe completed quickly, often employ EIA technology. Although less sensitive andspecific than laboratory EIA and DFA tests, they have been useful in the detection of C. trachomatis infections of the eye.
DNA and RNA Detection: Chlamydia can be identified by detecting its nucleic acids (DNA or RNA). Initially,direct detection of nucleic acid was performed withoutits amplification. Newer techniques amplify the nucleic acid, making the detection of very low amountsof DNA or RNA possible.These tests are therefore farmore sensitive than prevous tests and show comparable sensitivities for male and femaleurine, urethral and cervical swab specimens.
Antibody Detection in Serum: Different serological assays have been developed for the detectionof antibodies to C. trachomatis, including the complement fixationtest, micro-immunofluorescence assay, EIA and immunoblotting.Superficial infections stimulate poor antibody responses, however,a correlation between antibody levels and the severity of inflammation has been shown. IgG antibodies persist for years even after antibiotic treatment. Chlamydia IgG antibody testing in serumis often used in patients undergoing treatment for infertility, but it has no value in early diagnosis and national screening programmes.