Presumptive diagnosis of gonorrhoea is made on finding Gram-negative intracellular diplococci in a smear of the discharge. In men, microscopy of urethral smears is more sensitive in symptomatic (90–95%) than in asymptomatic (50–75%) patients. In women sensitivity of microscopy of Gram-stained endocervical smears is around 50%. Microscopy is not appropriate for pharyngeal and rectal specimens.
Confirmatory diagnosis is made by identification of the organism on selective culture media.
NAATs (PCR) are more sensitive than culture and can be used as diagnostic/ screening tests on non-invasively collected specimens (urine and self-taken vaginal swabs). The sensitivity of NAATs is >90% for genital sites, whilst the sensitivity of culture may be < than 75% for endocervical swabs.
There are currently no NAATs licensed for use with rectal or pharyngeal samples, although studies suggest that the sensitivity of NAATs at non-genital sites exceeds 90% whereas the sensitivity of culture can be <60% for rectal swabs and <50% for pharyngeal swabs.
The DSC clinic currently uses NAATs to detect rectal, urethral and cervical GC, and cultures for pharyngeal GC.
Some degree of caution is required in interpretation of positive results as the specificity of NAATs is not 100%; especially if the risk profile of the patient is at odds with the result. Confirmation of a NAAT positive result by culture can be considered in cases where there is some doubt. However, generally NAATs are considered reliable for detection.
As nonculture tests cannot provide antimicrobial susceptibility results, in cases of persistent gonococcal infection after treatment, clinicians should perform both culture and antimicrobial susceptibility testing.
Gonococcal complement fixation test (GC-CFT) should not be used for diagnosing gonorrhoea.
Routinely from the urethra; rectal and/or oropharyngeal tests when indicated by sexual activity. FVU provides an alternative urethral specimen for testing with a NAAT.
Routinely from endocervix if speculum examination performed; and rectal and oropharyngeal tests when indicated by the sexual history. Urine or a self-taken vaginal swab are suitable alternative specimens as screening tests using a NAAT.