From the Guidelines
The most effective Human Immunodeficiency Virus (HIV) blood test is the 4th generation antigen/antibody combination test, which can detect HIV infection as early as 2-4 weeks after exposure. This test looks for both HIV antibodies (your body's response to the virus) and the p24 antigen (a viral protein present before antibodies develop), making it more accurate for early detection than older antibody-only tests 1. The 4th generation assays incorporate HIV p24 antigen detection, allowing for earlier diagnosis of infection, typically within four to seven days after detectable virus by NAAT 1.
Key Points to Consider
- The testing algorithm associated with the use of 4th generation assays does not require Western Blot, instead, individuals with reactive results are further tested with an antibody immunoassay that distinguishes HIV-1 from HIV-2 antibodies 1.
- If the differentiation assay is negative, further testing with a qualitative or quantitative NAAT is recommended to rule out acute HIV-1 infection 1.
- If the differentiation assay is positive, viral load testing (and usually also CD4 determination) is recommended to direct management 1.
- For the most reliable results, testing should be done at least 4 weeks after potential exposure, though waiting 3 months provides near-complete certainty.
- Regular testing is recommended for those at higher risk of HIV exposure, including sexually active individuals with multiple partners, people who inject drugs, and partners of HIV-positive individuals.
Importance of Early Detection
Early detection of HIV infection is crucial as it allows for prompt treatment, which can prevent progression to AIDS and reduce transmission risk to others. The 4th generation antigen/antibody combination test is widely available at healthcare providers' offices, clinics, and many pharmacies, making it easily accessible for those who need it.
Testing Recommendations
- The Association of Public Health Laboratories and the Centers for Disease Control and Prevention now recommend 4th generation assays as initial screening tests for diagnosis of HIV infection 1.
- An alternate approach is an initial HIV antigen/antibody combination assay that discriminates detection of antigen from antibody; p24 reactivity is subsequently confirmed by NAAT and antibody reactivity by an HIV-1/HIV-2 differentiation assay 1.
From the Research
HIV Blood Tests
The most effective Human Immunodeficiency Virus (HIV) blood test is a combination of tests, including:
- Enzyme-linked immunosorbent assay (ELISA) as the primary screening test 2, 3, 4, 5
- Western blot assay as a confirmatory test 2, 3, 4, 5
- Rapid immuno-chromatographic assays, such as Determine, SD Bioline, and Uni-Gold, which have been shown to have diagnostic accuracy comparable to double ELISA or double ELISA with Western Blot strategies 6
Characteristics of HIV Blood Tests
The characteristics of these tests include:
- ELISA: greater than 98% sensitivity and specificity for HIV 2, but may have false-positive and false-negative results 2, 5
- Western blot: reliable confirmatory test, but may also have false-positive results 3
- Rapid immuno-chromatographic assays: high sensitivity and specificity, with some assays having 100% sensitivity and specificity 6
Limitations and Considerations
It is essential to consider the limitations and potential issues with these tests, including: