Sample Collection and Transport
- For standard HIV-1/HIV-2 antibody testing, a single tube (10 mL) of whole blood is sufficient.
- Specimens can be stored at room temperature for up to 3 days, and at 4°C for up to 7 days.
- For longer storage periods, the serum or plasma must be separated from the clot or cells and stored at -20°C.
- Specimens for PCR generally need to be processed within 48 hours of the collection as viral DNA denatures over time and becomes undetectable.
- Point of Care tests (POCT) for HIV
These tests provide rapid, on-site HIV results in a format that is relatively easy to perform.
- ELISA for HIV diagnosis
It is commonly used as a screening assay for many infectious diseases, including HIV. It is a highly sensitive test but false positives can be seen. The current ‘window period’ (the time from exposure to seroconversion) for HIV is less than three weeks in most cases.
All HIV diagnostic laboratories must confirm repeated EIA screen-positive results (done by using different parts of the viral antigen ) by a confirmatory assay, usually with Western blot.
Specimens that screen positive in the first assay but negative in the second assay should still be considered for confirmatory testing if the patient is symptomatic or high risk.
- p24 antigen testing
p24 antigen tests are also enzyme immunoassay (EIA) based. Antibody is used to capture the disrupted p24 antigen from patient serum.
P24 antigen test is useful
- for specimens from patients that are high risk and symptomatic but HIV EIA-negative (for Ab testing), or
- for specimens that are EIA-positive but Western blot-negative or –indeterminate
- for confirmation of neonatal HIV infection
Western blot Test
Western blot is a confirmatory diagnosis of HIV infection. Western blot is a highly specific immunoblot that allows for the visualization of antibodies to the structural polypeptides of HIV.
Viral genome amplification (PCR)
- in the diagnosis of HIV infection in infants born to infected mothers (presence of maternal IgG antibodies excludes serological testing during the first few months after birth)
- resolving indeterminate Western blot results and
- testing immunocompromised individuals who may not mount an antibody response.