Promote and facilitate access to safe, reliable and appropriate in vitro diagnostic technologies and laboratory services in an equitable manner
CD4+ T-cells are also known as helper T-cells and act as an co-ordinator of the immune response, unfortunately, CD4+ T-cells are also the main targets of HIV. HIV destroys infected CD4+ T-cells and leading to an overall weakening of the immune system.
Lower numbers of circulating CD4+ T-cells indicates a weakening of the immune system and advancement in the progression of HIV disease. The CD4+ T-cell count can also be indicative of the success or failure of anti-retroviral therapy (ARV).
CD4+ T-cell counts are performed using manual and automated methods.
HIV-1 viral load refers to the number of viral particles found in each millilitre. The more HIV-1 viral particles in the blood, the faster the CD4+ T-cells are likely destroyed and the faster the progress toward AIDS.
CD4+ T-cell counts are used, together with the Viral Load test, to get a complete picture about how the immune system is fighting the virus. As HIV reproduces within the body, the viral load increases and HIV destroys the CD4+ T-cells and thus lowers the amount of cells present. Generally, the higher the HIV viral load, the more CD4+ T-cells are being destroyed. The goals are to keep CD4+ T-cell count high and viral load low.
The viral load test should consistently detect and measure virus levels down to 50 copies/mL, have a high specificity and provide reproducible results. The technologies used are advanced and very sensitive for measuring the amount of HIV genetic material present in the blood.
Enzyme-Linked Immunosorbent Assays (ELISAs) are the most widely used type of assay. They have evolved from viral lysate tests to tests containing recombinant protein and synthetic peptide antigens:
Simple/Rapid tests are designed for use where a preliminary screening test result is required and are especially useful in resource-limited countries
ELISAs are highly sensitive and specific, and are able to detect HIV-1/ HIV-2 and variants. They require sophisticated equipment that must be regularly maintained, a constant electricity supply and skilled technicians. They are really not suitable for small laboratories, but for testing large numbers of samples per day, as well as in blood banks or for surveillance studies. The Simple/Rapid tests are better for emergency testing, and in smaller laboratories with low numbers of tests per day.
What is a confirmatory assay?
Confirmatory Assays are used to confirm whether specimens found reactive with a particular screening test contain antibodies specific to the virus they have been tested for.
This is the time between original infection with HIV and the appearance of Detectable antibodies to the virus, normally a period of about 14-21 days.
Tests are currently available for anti-HIV testing using urine and saliva specimens. However, the level of antibodies in these specimen types is lower than serum or plasma. Therefore, rigourous sample collection conditions, testing procedures, result validation and interpreation must be followed.