Laboratory Studies
Traditional tests
Wet mount of the discharge usually demonstrates more than five white blood cells (WBCs) per high-power field (HPF). Most practice guidelines recommend a polymorphonuclear leukocyte (PMN) count of 10-30/HPF as the threshold value to support the diagnosis of mucopurulent cervicitis. However, the leukocyte criterion is not standardized, and inflammation alone is not considered presumptive evidence of chlamydial infection.
Gram stains of the cervical mucus may reveal gram-negative intracellular diplococci in cases of gonorrhea. Culturing in modified Thayer-Martin medium is the criterion standard for confirming gonorrhea.
Enzyme-linked immunosorbent assay (ELISA) or direct fluorescent antibody testing is often used to detect chlamydial infection. DNA probes with 90-97% sensitivity are also available for the simultaneous detection of gonococcal and chlamydial organisms.
When indicated, chlamydial cultures are performed on McCoy cells (evaluations in prepubertal children in whom sexual abuse is suspected, testing response to therapy in a previously treated infection).
Nucleic acid amplification tests
Several highly specific and sensitive tests have been developed. These nucleic acid amplification tests (NAATs) include the polymerase chain reaction (PCR), the ligase chain reaction (LCR), [14] and transcription-mediated amplification (TMA). [15] Probes used in these tests are at least 20% more sensitive than the earlier DNA probes and are the tests of choice. PCR and LCR testing consists of amplification of specific DNA sequences, whereas TMA testing is an RNA amplification assay.
Although endocervical specimens are preferred, these tests may be easily performed on first-void morning urine samples as well as on vaginal and cervical samples. Urine NAATs are highly sensitive for the diagnosis of endocervical chlamydial infection.
Other Tests
Because of the possible association between bacterial vaginosis and mucopurulent cervicitis, the NAATs described above should be performed. In addition, Amsel criteria for the diagnosis of bacterial vaginosis should be sought. The presence of three of the following four criteria suffices for the diagnosis of bacterial vaginosis:
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Homogenous vaginal discharge
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Vaginal fluid pH greater than 4.5
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Clue cells greater than 20% of total vaginal epithelial cells on ×100 magnification
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Amine odor on addition of potassium hydroxide to vaginal fluid
