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Diagnostic Tests For Chlamydial Infection.
Because symptoms, examination findings, and microscopy do not reliably distinguish chlamydial infection from other organisms causing the same syndromes, patients suspected of having genital chlamydial infection should have specific diagnostic testing for C trachomatis. Confirmation of chlamydial infection is important for purposes of patient treatment, patient education, sex partner treatment, and for communicable disease reporting (to monitor the prevalence of chlamydia). Many different diagnostic assays are available for detection of C trachomatis. These vary in terms of test sensitivity, cost, and patient convenience.

Screening Recommendations
Populations with the greatest risk for genital chlamydial infection, yet who have unrecognized chlamydial infection, should also undergo chlamydial screening. The CDC and the US Preventive Services Task Force each currently recommends annual chlamydial screening for all sexually active women 25 years of age and younger, as well as for older at-risk women (eg, with new or multiple sex partners). The importance of annual chlamydial screening for young women is further emphasized by the inclusion of such screening as an element of the Health Plan Employer Data and Information Set (HEDIS) measures widely used to compare the quality of health care provision. The benefits of chlamydial screening have been demonstrated in parts of the United States where screening and treatment programs for women have reduced both the prevalence of infection and PID rates. Although no guidelines have been provided for chlamydial screening in men, consideration should be given for screening men 25 years of age and younger or those at higher risk if resources permit, especially in clinical populations with a high prevalence of disease.

Nonculture Tests
Chlamydia culture has been the reference standard against which all other tests have been compared. However, nonculture tests are now far more commonly used because they are less technically demanding and may be less expensive and or more sensitive than chlamydia culture.

The earliest nonculture screening tests for C trachomatis were based on detection of chlamydial antigen, rather than growth of the organism, and included enzyme immunoassays and direct fluorescent antibody tests. Nucleic acid hybridization tests (ie, DNA probes) then became available. These nonculture tests were less expensive and less technically demanding than culture; however, they also had lower test sensitivities and therefore failed to detect infections more often than culture, with the exception of direct fluorescent antibody testing, the sensitivity of which was similar to culture. Serologic assays for chlamydia have also been available yet are not widely used in the diagnosis of urogenital chlamydial infection because they do not distinguish past from current C trachomatis infection; cross-reacting antibody can occur with infections caused by other chlamydial species (eg, C pneumoniae); they may be negative in early or acute chlamydial infection, especially in men presenting with symptomatic nongonococcal urethritis (NGU); and titers are often low with superficial mucosal infections.

NAATs became available for routine clinical use in the mid 1990s and are the preferred and recommended means for detecting C trachomatis infection. These tests offer two distinct advantages over culture or earlier nonculture-based chlamydia tests: (1) higher test sensitivity (approximately 15–20% higher than former tests), resulting from the amplification of nucleic acids, thereby improving the likelihood of detecting the organism (especially when the bacterial burden is low); and (2) greater patient convenience or satisfaction by using noninvasively collected specimens, including urine, tampons, or self-collected vaginal swabs. Hence, NAATs can facilitate chlamydia screening outside of conventional clinical settings. One disadvantage of NAATs is their higher cost. However, the higher test sensitivity may still allow NAATs to be more cost-effective than other chlamydia tests as their use may decrease the prevalence of genital chlamydia or PID.

Additional Tests for Coinfection
Most individuals undergoing testing for chlamydia should also receive testing for gonorrhea, because coinfection with both organisms is common and their recommended treatments differ.