Serology and viral load testing for CMV, EBV, hepatitis, HIV and syphilis
What IgM, IgG, avidity, antigen and nucleic acid tests each tell you, window periods, a step-by-step way to read CMV, hepatitis B and C, HIV and syphilis results, positive predictive value in low-prevalence testing, and how to read HIV, HBV, HCV and CMV viral loads and decide whether a change is real.
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
- Serology measures the host response: IgM suggests recent infection, IgG shows exposure at some point, and IgG avidity dates a primary infection. Antigen and nucleic acid tests (NAT, PCR) detect the organism and show current infection.
- Every antibody test has a window period. If the exposure was recent and the result negative, repeat it or add NAT.
- Viral load (quantitative NAT) shows how much virus is replicating. It drives treatment decisions in HIV, HBV and transplant CMV, and only needs to be qualitative for HCV.
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Sources
- National HIV Testing Policy (types of HIV testing, window period, point-of-care and self-testing)AU/NZASHM, endorsed by BBVSS, current online version (checked November 2026)
- National Hepatitis C Testing PolicyAU/NZASHM, endorsed by BBVSS and PHLN, version of 5 June 2025, effective July 2025
- National Hepatitis B Testing PolicyAU/NZASHM, endorsed by BBVSS, effective 18 February 2021; s100 prescriber accreditation for HBV medicines removed from 1 September 2026
- Australian National Guidelines for HIV Post-Exposure Prophylaxis (4th ed.): laboratory assessment and follow-upAU/NZASHM, 2025 (last updated August 2025)
- Australian STI Management Guidelines for Use in Primary Care: syphilisAU/NZASHM, updated October 2026
- RCPA Manual: pathology tests (CMV serology and avidity, HIV, hepatitis and syphilis tests)AU/NZRoyal College of Pathologists of Australasia, online edition (individual entry dates vary)
- Leruez-Ville M et al. Consensus recommendation for prenatal, neonatal and postnatal management of congenital cytomegalovirus infection from the European congenital infection initiative (ECCI). Lancet Reg Health Eur 2024;40:100892European congenital infection initiative, 2024
- Kotton CN et al. The Fourth International Consensus Guidelines on the Management of Cytomegalovirus in Solid Organ Transplantation. Transplantation 2025;109(7):1066-1110Transplantation Society International CMV Consensus Group, 2025
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy