4th-generation Ag/Ab is first-line and reliable from ~18 days, definitive by 45 days. Offer testing opportunistically at every appropriate visit, test higher-risk groups more often, and don't miss acute seroconversion — it's easily mistaken for a viral illness.
Who to test
- Routine offer: new patient registration, antenatal care, any STI presentation, blood-borne virus screen.
- MSM: at least annually; 3-monthly if on PrEP or with multiple partners.
- People who inject drugs: at least annually; co-test for HCV/HBV; offer needle and syringe program information.
- Higher prevalence: birth in a high-prevalence country, sex workers, sexual partners of a person with HIV.
- Clinical clues: unexplained weight loss, lymphadenopathy, oral thrush, shingles under 50, recurrent infections, new TB.
Diagnostic algorithm
4th-generation Ag/Ab is the first-line test.
14th-gen Ag/Ab: ELISA for p24 antigen + HIV-1/2 antibodies; window ~18 days, reliable by 45 days; no referral needed to order.
2Confirmatory: if reactive, an HIV-1/2 antibody differentiation assay — most Australian labs auto-run this.
3RNA PCR: if indeterminate or acute HIV suspected; detects from ~10 days; also a baseline test before ART.
Acute HIV — don't miss it
- Classic seroconversion, often mistaken for a viral illness: fever, generalised lymphadenopathy, pharyngitis, a maculopapular rash on the trunk and face.
- Also common: myalgia/arthralgia, painless oral or genital ulcers, headache or meningism, diarrhoea, weight loss.
- Symptoms 2–4 weeks post-exposure: order HIV RNA PCR directly — don't rely on 4th-gen Ag/Ab alone; viral load is often very high.
- Refer same day for specialist review if neurological signs, severe pharyngitis, or profound symptoms.
Window periods by test type
- 4th-gen Ag/Ab: detects from ~18 days, reliable by 45 days — standard first-line, used by most Australian labs.
- HIV RNA PCR: detects from ~10 days, reliable by 10–14 days — use for acute or recent exposure under 6 weeks.
- 3rd-gen antibody-only: detects from ~25 days, reliable by 12 weeks — an older test, avoid as first-line.
- Rapid point-of-care: detects from ~18 days, reliable by 45 days — self-test kits, not Medicare-rebatable.
Testing access & resources. ASHM helpline 1800 022 226 for clinician support. No referral is required to order an HIV test. Confirm current MBS testing item numbers at mbsonline.gov.au.
Safety
- Don't rely on a 4th-generation test alone if acute HIV is suspected — order HIV RNA PCR directly, as the antibody response may not yet be detectable.
- Discuss the result-disclosure process before testing, even though no specific consent form is required beyond standard pre-test discussion.
- Test higher-risk groups more than once a year — 3-monthly for MSM on PrEP or with multiple partners.
Red flags / refer
- Severe or profound seroconversion symptoms, neurological signs, or inability to swallow → same-day specialist review.
- A reactive 4th-generation result → same-day referral to an HIV physician or sexual health clinic (see the companion Results & Notification sheet).
- Suspected acute HIV in pregnancy → urgent co-management with obstetrics and an HIV physician.
ID-01 v1.0 · Reviewed Jun 2026 · Review Jun 2027
For health-professional use. Framework: ASHM HIV Testing Policy, Australian Department of Health. Companion sheet: ID-01B HIV Results & Notification. ASHM helpline 1800 022 226.
