[Question #453] confused about my HIV test

77 months ago
Hello experts!

I have recently had a bit of a scare which I will describe as follows. 10 weeks ago I had unprotected sex, and 6 weeks ago I gave unprotected oral (no ejaculation) unprotected. Since then I have tested 3 times. The most recent test being negative at 10 weeks past the unprotected penetrative sex, and 6 weeks past giving unprotected oral. 

I took this test in Australia so I am unsure of the specivity of it except that it said it was 'HIV 1/2 Antigen and Antibody'. Given that 3 months has not elapsed since this risk I am concerned about how conclusive this test is.

I am aware that your stance on this forum...along with other Doctors such as Dr Hook, Dr Sean and Dr Jose is that if somebody receives a negative 4th Gen test past 28 days that it is deemed conclusive. However it is my understanding that a 4th gen test looks for the p24 antigen aswell as antibody. My test is just called  'HIV 1/2 Antigen and Antibody'. Because it doesn't state it looked for the p24 antigen..does this mean it is not conclusive till 3 months? Perhaps the antigens my test looked for are not p24..and therefore take up to 3 months to appear? 

To summarise, given my test is just called  'HIV 1/2 Antigen and Antibody' (and does not mention p24 antigen), does the 3 month window period still stand? I am sorry to put you through the banality of answering yet another one of these worry wart questions. I also apologise for sounding so uneducated and obsessively worried. 

Even in the most high risk of situations..would you still tell a patient that a negative 4th gen was conclusive at 28 days past exposure?

Thank you so very much for your time

Edward W. Hook M.D.
77 months ago

Welcome to our Forum.  Irrespective of the type of exposure, a negative 4th generation test for HIV at 4 weeks/28 days provides virtually absolute assurance that you did not acquire HIV.  The ONLY exception to this is for persons who have taken anti-HIV medications in efforts to prevent an infection (i.e. PEP).  In all cases, the "antigen" referred to in the description is a p24 antigen.  No need to seek further testing beyond the time of a 4 week test.

I hope this comment is helpful.  EWH

77 months ago
Thank you for your response Dr Hook. 

So you're saying a test such as mine called 'HIV 1/2 Antigen and Antibody' would be considered a 4th gen/duo/ combo?

If so, you say that this is conclusive at 4 weeks (regardless of risk)..but how can this be the case when I have found this quote from Dr Handsfield 

"On this forum, our replies about when to test do not depend only on the test reliaibility, but on the overall context.  If someone has only 1 chance in 100,000 of having caught HIV, a negative test at 4 weeks (90% reliability) drops those odds to 1 in a million.  That's close enough to zero that such a person doesn't really need additional testing, except for psychological reassurance.  On the other hand, if the exposure was high risk and the odds s/he caught HIV are, say, 1% (1 in 100) a 4 week test drops that chance to 1 in 1,000.  That's helpful, but not good enough.  That person needs testing at 6-8 weeks and perhaps 3 months.  Same test but different situations, therefore different testing advice"

Admittedly that phrase was from 2011..but this clearly states that some people need to test till 3 months (if risk is high). 

I'm sorry to get into an issue of semantics but I'm really just trying to ascertain how conclusive my test was. It is very daunting waiting such a long period. 

Kind regards


Edward W. Hook M.D.
77 months ago
You are getting caught up in semantics and are quoting statements that are nearly five years old.  The test you describe was a 4th generation tests which provides (for you and anyone else tested) conclusive results at 4 weeks after an exposure.  You need to believe your test results.  Further concern about this exposure, like further testing is a waste of your time and resources.  EWH---
77 months ago
Hi again Dr Hook,

For my final comment I'd just like to ask quickly about a second window period.

I found this statement from this CDC document -  http://www.cdc.gov/hiv/pdf/HIVtestingAlgorithmRecommendation-Final.pdf

"Rare cases of a “second window” during early seroconversion during which antigen/antibody combination tests transiently revert to nonreactive have been reported outside the United States with older versions of 4th generation tests than those that are FDA-approved.119-121 One case of a “second window” of 8 days’ duration was observed in a study of 28 patients in Africa and Thailand with acute, non-B subtype HIV infections identified by frequent RNA testing.122 Subsequent testing was conducted with immunoassays and viral load assays at frequent intervals. In this case, an FDA-approved 4th generation assay became reactive for antigen at day 9 after RNA detection, was subsequently nonreactive between days 17-25, and became reactive again at day 29 when antibody levels, detected by a 3rd generation assay, began to rise. Presumably, this phenomenon was due to the short interval when antibodies begin to appear during which antigen bound to antibody inhibits detection of either antigen or antibody by the assays. Experience with the FDA-approved 4th generation immunoassays is too limited to predict whether or how often transient seroreversion might occur in patients with subtype B infections"

What are your thoughts on second windows? Do you think they can occur on 4th gen tests that aren't FDA approved and less sensitive (i.e. outside the USA).

Thank you
77 months ago
I forgot to add........do you think that different 4th gen tests perform differently depending on the manufacturer?

Would you say that SOME 4th gen tests are conclusive at 4 weeks whilst others may not be as sensitive?
Edward W. Hook M.D.
77 months ago

As indicated in the quote you include, these events are TRANSIENT.  They are theoretically possible and when they occur, they last only a few days.  You indicate you have been tested three times- in this case your negative tests would not indicate a "2nd window" and should be believed.  Further, please understand because, as a quasi-political organization, agencies like the CDC feel they cannot "afford" to be wrong and therefore tend to be highly conservative and list virtually every possible exception in an effort to not be wrong.  None of this in any way changes my assessment of your situation or advice to you.

All 4th generation tests must perform to the same standard to become FDA approved, irrespective of the manufacturer.  ALL are conclusive at 4 weeks,

This is my third reply to your questions.  As per Forum policy, later today this thread will be closed.  Take care.  EWH