Investigations for common STIs
What culture, NAAT and serology each tell you in sexual health, the right sample for each site, reading syphilis and HIV results step by step, resistance testing for gonorrhoea and Mycoplasma genitalium, window periods and test-of-cure timing under ASHM guidance.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Three kinds of test answer different questions. NAAT (PCR or TMA) finds organism nucleic acid with high sensitivity. Culture grows the organism so it can have susceptibility testing. Serology finds the antibody response and is the main test for syphilis, HIV and hepatitis.
- In Australia NAAT is the first-line test for chlamydia, gonorrhoea, Trichomonas and M. genitalium. Culture is kept for gonorrhoea susceptibility and some ulcers.
- The commonest errors are the wrong sample, testing inside the window period, and doing a test of cure too early.
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Sources
- Australian STI Management Guidelines for Use in Primary Care: gonorrhoea, chlamydia, Mycoplasma genitalium, trichomoniasis, syphilisAU/NZASHM (Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine), Current online edition, checked November 2026 (draft Australian Contact Tracing Guidelines 2026 in consultation until 2 December 2026)
- National HIV Testing Policy and ASHM HIV guidelinesAU/NZASHM, Current online edition, checked November 2026
- Therapeutic Guidelines: Sexual and reproductive healthAU/NZTherapeutic Guidelines Limited (eTG complete), current eTG edition (topic version not verified)
- Workowski KA et al. Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep 2021;70(4):1-187Centers for Disease Control and Prevention, 2021 (still the current CDC edition, November 2026)
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Turnstile bot check on sign-in and signed-out feedback