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Different types of Available HIV test
- Combined antibody-antigen tests. (Combo)
- Viral load tests (RNA PCR test)
Combined antibody/antigen tests (Combo)
These are called 4th generation tests or combined antibody/antigen (Ag/Ab) tests. In these tests, the antigen being tested is a major HIV protein called p24.
P24 (short for protein 24) is produced 2–3 weeks after infection and before antibodies are produced. p24 levels are only detectable for the next 1–2 months. However, by the time the p24 levels have dropped antibodies will be present.
4th generation (Ag/Ab) tests are recommended four weeks after exposure. They give an earlier result than antibody-only tests that are recommended after six weeks. Detecting over 95% of infections at four weeks after exposure.
As small percentage of people (less than 5%) may have a delayed response to HIV.
Viral load (RNA PCR) test
This test looks directly for HIV in blood, and can be used from 3 days to 4 weeks after an exposure.
After infection, viral load is usually very high within the first 4 weeks, and so this test can be used to confirm a suspected early infection if someone has symptoms.
However, some people have undetectable viral load without treatment, so a negative result does not guarantee that you do not have the virus.
When can each test be used?
Antibody/Antigen (Combo) is recommended four weeks after exposure because it will detect 95% of infection.
After a potential exposure, HIV viral load can be detected in most people 7-14 days after infection. In 95% of cases viral load will be detected between 3 days and 6 weeks.
4th generation HIV antigen/antibody tests will detect 95% of infection after 4 weeks. Detecting more than 99.999% of infection after 90 days.