Is the rapid HIV P24 Antigen/Antibody Combo or Duo test conclusive at 28 days? CDC HIV Guidelines

Part 2

“The 2014 CDC Guidelines”

Now what about the latest guidelines concerning HIV Testing?

Some of my patients have observed,

“There are certain websites that allege they have the latest information and guidelines, and these claim that the latest, most up-to-date guidelines teach that the rapid HIV Combo/Duo test is conclusive when performed at 28 days.”

Surely you couldn’t argue with the latest, most up-to-date information portals, can you?

In fact, I often respond, “If there is such a guideline making such a claim, please furnish me with a copy. It makes my job much easier.”

One of the most up-to-date HIV testing guidelines to be published is by the Centers for Disease Control and Prevention (CDC), “Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations,” which was published June 27, 2014.

According to the CDC latest HIV testing algorithm, the new HIV testing recommendations advise a sequence of tests used in combination, starting with a fourth-generation HIV test. So we, physicians, are supposed to start with a 4th generation HIV antigen/antibody combination test.

What is more? If this initial test is negative, no further testing is needed.

Couldn’t it be simpler? We start with the HIV Combo/Duo test, and if that is negative, no further testing is required. It is conclusively negative.

Do we need any further evidence?

In fact, page 7 of this latest guideline says:

“Laboratories should conduct initial testing for HIV with an FDA-approved antigen/antibody combination immunoassay that detects HIV-1 and HIV-2 antibodies and HIV-1 p24 antigen to screen for established infection with HIV-1 or HIV-2 and for acute HIV-1 infection. No further testing is required for specimens that are nonreactive on the initial immunoassay.” (emphasis mine)

So on the surface, it seems apparent that a negative 4th generation HIV Combo/Duo test would be conclusive, and “no further testing is required.”

If this interpretation is true, then my job is really much simpler and easier.
What are CDC’s actual recommendations?

Careful study of this page (page 7) from the latest guideline would reveal a footnote which reads:

“Exception: As of April 2014, data are insufficient to recommend use of the FDA-approved single-use rapid HIV- 1/HIV-2 antigen/antibody combination immunoassay as the initial assay in the algorithm.”

What does it say? The CDC does not recommend the “single-use rapid HIV- 1/HIV-2 antigen/antibody combination immunoassay” in its algorithm.

And just in case we missed it, it’s repeated again later in the guidelines.

Let’s peruse page 17 of the guidelines. Again, CDC says, “Laboratories should conduct initial testing for HIV with an FDA-approved antigen/antibody combination (4th generation) immunoassay …”

It says, “laboratories should.” Obviously, this doesn’t refer to rapid point of care tests (POCT).

A footnote on the same page (page 17) writes:

“Exception: As of April 2014, data are insufficient to recommend use of the FDA-approved single-use rapid HIV- 1/HIV-2 antigen/antibody combination immunoassay as the initial assay in the algorithm.”

What does it say? The CDC does not recommend the “single-use rapid HIV- 1/HIV-2 antigen/antibody combination immunoassay” in its algorithm, and the CDC repeats it twice just in case we missed it the first round.

Megan Brooks, in her article “New CDC HIV Testing Recommendations Offer Faster Diagnosis” writes:

“The new recommendations are based on both HIV tests approved by the US Food and Drug Administration (FDA) as of December 2012 and “scientific evidence, laboratory experience, and expert opinion” collected from 2007 through December 2013, the CDC says.

“These recommendations do not include the rapid HIV-1/HIV-2 antigen/antibody combination test approved by the FDA in August 2013 (for which evidence of performance in the algorithm was insufficient) or HIV-2 nucleic acid tests…which lack FDA approval,” they [the CDC] note.” (emphasis mine)

Ms Brooks recorded the same observation – the new CDC HIV testing algorithm does not include “the rapid HIV-1/HIV-2 antigen/antibody combination test,” “for which evidence of performance in the algorithm was insufficient.”

In case you are wondering what Medscape is, it is a doctor’s education portal.

Surely you couldn’t argue with the latest, most up-to-date information portals, can you?
Conclusion

The rational behind the new CDC Guidelines is not very complicated. Studies have shown that the highest rate of HIV transmission occurs during a period of p24 antigenemia (generally detectable 2 to 3 weeks after initial exposure) that precedes the development of detectable anti-HIV antibodies. These anti-HIV antibodies may take 3 to 12 weeks to develop to detectable levels. The CDC hoped that the ability to detect HIV infection during this early window period may help to slow the rate of HIV transmission among the population.

So, yes, we can conclusively say that the UK National Guidelines for HIV Testing and the CDC’s very own guidelines do not make the claim that the rapid 4th generation HIV antigen/antibody combination test is conclusive at 28th days post exposure. These guidelines actually agree in that point.

If in doubt, please confer with your doctor or a HIV Specialist concerning these HIV tests. I hope my articles do not serve to confuse you any further.

Please talk to our Family Physician in Singapore concerning HIV Testing and STD screening.

Furthermore, if you have exposed yourself to the HIV virus within the last 72 hours, do consider visiting our Family Physician in Singapore for HIV Post Exposure Prophylaxis (HIV PEP).