Ask you doctor about the tests he used.
He wasn't able to answer my questions because he doesn't know much about it he told me...
I saw some people on this forum have a lot of knowledge regarding this subject, so I was hoping someone could help me out.
Go and read this. If you try using google for questions like this it is very usefull.
Let us understand how the duo tests work.
A duo test has a mechanism that looks for two indicative materials simultaneously. Viz; HIV antibodies and P24 antigen production.
Now, for an individual who is actually infected, will go through the below listed phase:
Sero-conversion : A gradual process of the body getting acustomed to the alien material, in this process, the imune system of the body fights the alien matter until detectable amount of antibodies are present. During this transition, the phase when detectable amount of antibodies are not present, body releases an enzyme called as p24. The whole process of sero-conversion is completed within 7 to 14 days after infection. One week preeceding sero-conversion, detectable amount of antibodies are almost always present.
Now, with the aforesaid details, a IV gen test is recommended at the 6th week, to rule out the the risk of late seroconversion (Happens in a very few number of people, usually people on chemotherapy or PEP). At this point, the test looks for two specific things. One, if late sero conversion P24 and if already seroconverted, antibodies. Most of the time the antigen part of the test is irrelavant because practically, at the 6th week it's pretty difficult for some one to sero convert. Hence, your doctor said ''antigen part was omitted''. The test principally is administered for antibody detection but with caution of ruling speculations for slow seroconversion.
Now, let's relate your situation here-
1.You have been adminstered on a valid test. It is a duo test, IV gen testing, that looks for antibody and antigen simultaneously.
2.Your doctor was right. Because the time that you had taken this test had already surpassed the phase of P24 production inside your body, if you were infected at the first place. Hence, at the juncture you tested, if there was P24 production it would have been detected, which is practically impossible. However, the antibody detection was also negative, that rules out HIV from the core.
3. I am assuming that you perhaps tested at the 12th week, at that point a 3rd gen antibody (4gen minus the p24 antigen)would have been good. However, your doctor might have chosen to be conservative and decided to administer you on 4th gen and there is no harm to it because the end result is accurate and same. Now this also explains your last question, difference between the 3rd and the 4th gen is basically, 3 gen anti body test plus p24 antigen testing is 4 gen test.
Hope this helps.
There are no tests marketed or sold to give a conclusive negative test earlier than 3 months post esposure.
Current methods for the detection of HIV may not detect all infected individuals. An ARCHITECT HIV Ag/Ab Combo test result that is nonreactive does not exclude the possibility of exposure to or infection with HIV-1 and/or HIV-2. Nonreactive results in this assay for individuals with prior exposure to HIV-1 and/or HIV-2 may be due to antigen and antibody levels below the limit of detection of this assay.
UK testing guidelines.
The need for a repeat HIV test if still within the window period after a specific exposure should be discussed. Although fourth generation tests shorten the time from exposure to seroconversion a repeat test at three months is still recommended to definitively exclude HIV infection.
Thanks very much Mike for your usefull information.
It has been 18 days now since my possible exposure and I have not gone for a test yet.
If I'm right, you say in my case it would possible for the Centaur Combo test to find any p24 antigens or antibodies if they're already there? At least it would find one of the two?
Yes, take the first one at the 6 th week to calm your nerves, as 6 weeks result changing ahead is difficult. Like Teak mentioned, take the final one at the 12th week for a conclusive one.