4th Generation: HIV Lab Testing in the Modern Era
Over the last 30 years, both the HIV epidemic and the diagnostic technology used to detect the virus have evolved. CDC first published guidelines for the diagnosis of HIV-1 in 1989, followed by HIV-2¹ diagnosis guidelines in 1992. Then in 2004, CDC published guidelines on the confirmation of rapid test results.
These diagnostic algorithms all relied on screening specimens with an enzyme immunoassay (EIA) and confirming their results with either a Western Blot (WB) or an indirect immunofluorescence assay (IFA). What’s important to keep in mind is that these previous algorithms were able to detect the amount of antibodies in a patient—i.e. They were detecting a patient’s response to infection. They could not however, detect the virus itself, or what’s referred to as an antigen or nucleic acid test. There is a big delay in detecting a patient’s response to the virus compared with detecting the virus itself. This resulted in patients who had acute or early HIV and were at the highest risk of transmitting the virus not being detected as HIV positive. Missing people with early infection with the old algorithm allowed a lot of transmission to continue. Now, that can be prevented.
Since 2004, advances in diagnostic technology that detect both HIV antibodies and antigen (a patient’s response to the virus and the virus itself) have resulted in simpler rapid tests, more sensitive and specific laboratory-based tests, and tests capable of differentiating between HIV-1 and HIV-2. In 2014, CDC released updated guidelines that include these new diagnostic technologies and addresses the importance of detecting early infections. The San Francisco Public Health Laboratory recently implemented this updated algorithm and screens all HIV specimens with a fourth-generation antigen/antibody combo assay, confirms positive results with an HIV 1/2 differentiation assay (MultiSpot), and resolves discordant results with an individual HIV viral load assay.
You can find all of CDC’s testing guidelines, FDA-approved tests, and other resources here.
On May 7th, 2015, I’ll be hosting a webinar that will explore the history of HIV testing diagnostics and where we stand in the current algorithm from a lab perspective. If you’ve ever wondered how a lab works and what the challenges and opportunities are that labs face with the new HIV testing algorithm, you’ll want to join in on this conversation! Some other questions I’ll talk about are:
- What is the difference between a 1st, 2nd, 3rd and 4th generation HIV test?
- Why is it so critical to detect HIV earlier in infection?
- How do CLIA regulations affect where testing can be done (waived, moderate complexity, high-complexity)?
- What does HIV “confirmatory” testing mean exactly?
- What is the cost-benefit of the new testing algorithm?
- How does rapid HIV testing fit into the new algorithm?
You can also join the conversation on Twitter by following the hashtag #SFLabTalk.