Clinical Immunology and Serology
Domain focus
Clinical immunology and serology questions test immunoassay principles, HIV and syphilis testing algorithms, dengue serology, autoimmune markers and the interpretation of antibody and antigen results in the Cambodian laboratory.
Core rules
- Follow the national testing algorithm; a reactive screening test is confirmed by a second assay of different format or by nucleic acid testing.
- Interpret serology with the clinical stage and window period; IgM does not always mean acute infection.
- Use appropriate controls and check for prozone in high-titre samples.
- Do not report HIV status on a single reactive rapid test.
- For dengue, NS1 antigen is useful early; IgM rises later and may cross-react with other flaviviruses.
Worked example
A 28-year-old pregnant woman has a reactive first rapid HIV test and a non-reactive second test. Do not report HIV-positive. The reasoning: discordant rapid tests may reflect a false-positive first assay or early infection during the window period. Repeat on a new sample, perform a third assay or nucleic acid test, and provide counselling. Only a confirmed result is reported.
Traps
- Reporting a single reactive HIV rapid test as positive.
- Ignoring prozone in syphilis or dengue serology.
- Interpreting vaccine-induced antibodies as natural infection.
- Using IgM alone to date dengue infection.