Diagnostic Use
Screening for HIV infection is recommended for all patients seeking assessment for STIs, all patients initiating treatment for tuberculosis, all women receiving preconception advice and during each pregnancy. Regular screening (i.e. at least annually) is recommended for people likely to be at high risk for HIV infection. This includes injecting drug users and their sex partners, people who exchange sex for money or drugs and sex-partners of HIV-infected persons.
Diagnostic testing for HIV infection is recommended for all patients with signs or symptoms consistent with HIV infection or an opportunistic illness characteristic of AIDS.
Interpretation
Any results with reactivity in the screening test require supplementary testing before a diagnosis of HIV can be confirmed or excluded. One of the Clinical Microbiologists will notify the requesting team regarding any reactive result.
For patients with high-level reactivity in the screening test (suggestive of established infection), an HIV-1 qualitative PCR will be reflex tested by the Laboratory if EDTA blood is available and this is the first reactive test.
Possible causes of low-level reactivity in the screening test are seroconversion or non-specific (false-positive) reactivity. In this situation, HIV-1 PCR will be reflex tested by the Laboratory if EDTA blood is available. Repeating the screening test after 7-14 days is also recommended. A lack of increasing reactivity in the screening test supports non-specific reactivity. False-positive reactivity in the Roche screening test occurs in approx 1 in 1000 HIV tests.
A reactive screening test in an infant less than 18 months of age may represent maternally-acquired antibodies.
Test Method
Principle: 2-step antigen/antibody Sandwich Immunoassay
Reagents: Siemens Atellica IM HIV Ag/Ab Combo (CHIV)
Analyser: Siemens Atellica IM
Limitations / Interference
Patient samples may contain heterophilic antibodies that could react in immunoassays to give falsely elevated or depressed results.