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Confusion over different tests - clarified I think.
I posted on here about generation of tests in UK and what test detects what etc. I apologise to Teak and Liz for some of my frustrated responses, I think they mainly stemmed from my lack of knowledge about testing. So thought i'd post what I now know, (or atleast hope I am correct on). I've split it into numbered paragraphs just because it's quite long.
1) As I now believe, in the UK an ELISA test is used, either third or fourth generation. A third generation test, tests for antibodies in the blood, that if present will then lead to a further Western Blot test for confirmation. A fourth generation test is a test that looks for antigens as well as anitbodies in the blood. Antigens are proteins that the virus produces.
2) A fourth generation test is also known as a DUO or Combi HIV test. Most people seem to think that the DUO or Combi test means that the test looks for HIV1 and HIV2. This is not the meaning, the meaning is that it looks for anitbodies and antigens.
3) If you have a second, third or fourth generation ELISA test you are being tested for HIV1 and HIV2 from the single test (plus the subtypes of those strains). This I believe is another area of confusion; people keep mentioning the tests as though there is one ELISA test for HIV1 and another ELISA test for HIV2. This is not the case, a single ELISA test is looking for antibodies produced for HIV1 and HIV2. In the UK specifically I now know that whether a third or fourth generation test is used they are both testing for HIV1 and HIV2 antibodies (in the fourth generation the anitgen part is only detecting HIV1 I believe).
3) Using the third generation ELISA it is recommended that it should be taken at 3 months or more (UK recommendation) post possible exposure to get a conclusive result, although this is conservative and 6 weeks is recommended by Dr HHH and in France. This waiting time is known as the diagnostic window in which the anitbodies to HIV would be formed if one had aquired HIV.
4) Using the fourth generation ELISA it is recommended that it should be taken at 6 weeks or more as opposed to 3 months. This is the main advantage of a fourth generation test; that the diagnostic window is less. This is because antigens are produced faster than antibodies, so can be detected earlier. It is only antigens for HIV1 that are being looked for in the test. If one wants a test for HIV2 antigens this must be specified. The antibodies for HIV1 and HIV2 would again show after three months, just as with the third generation test - in fact the antibody part is the same test. This would again be conclusive for HIV1 and HIV2 from one test.
I thought my knowledge would help if anyones searching for such a thread, or have some of the confusions I encountered. I believe I am conpletely correct in what I have written. If not, or I'm completely right even, do say. Also if you'd like to add anything.
Regards Mike
1) As I now believe, in the UK an ELISA test is used, either third or fourth generation. A third generation test, tests for antibodies in the blood, that if present will then lead to a further Western Blot test for confirmation. A fourth generation test is a test that looks for antigens as well as anitbodies in the blood. Antigens are proteins that the virus produces.
2) A fourth generation test is also known as a DUO or Combi HIV test. Most people seem to think that the DUO or Combi test means that the test looks for HIV1 and HIV2. This is not the meaning, the meaning is that it looks for anitbodies and antigens.
3) If you have a second, third or fourth generation ELISA test you are being tested for HIV1 and HIV2 from the single test (plus the subtypes of those strains). This I believe is another area of confusion; people keep mentioning the tests as though there is one ELISA test for HIV1 and another ELISA test for HIV2. This is not the case, a single ELISA test is looking for antibodies produced for HIV1 and HIV2. In the UK specifically I now know that whether a third or fourth generation test is used they are both testing for HIV1 and HIV2 antibodies (in the fourth generation the anitgen part is only detecting HIV1 I believe).
3) Using the third generation ELISA it is recommended that it should be taken at 3 months or more (UK recommendation) post possible exposure to get a conclusive result, although this is conservative and 6 weeks is recommended by Dr HHH and in France. This waiting time is known as the diagnostic window in which the anitbodies to HIV would be formed if one had aquired HIV.
4) Using the fourth generation ELISA it is recommended that it should be taken at 6 weeks or more as opposed to 3 months. This is the main advantage of a fourth generation test; that the diagnostic window is less. This is because antigens are produced faster than antibodies, so can be detected earlier. It is only antigens for HIV1 that are being looked for in the test. If one wants a test for HIV2 antigens this must be specified. The antibodies for HIV1 and HIV2 would again show after three months, just as with the third generation test - in fact the antibody part is the same test. This would again be conclusive for HIV1 and HIV2 from one test.
I thought my knowledge would help if anyones searching for such a thread, or have some of the confusions I encountered. I believe I am conpletely correct in what I have written. If not, or I'm completely right even, do say. Also if you'd like to add anything.
Regards Mike
Yes good point, it would make interesting discussion.
Everything I wrote was all right and correct then?
Everything I wrote was all right and correct then?
UK TESTING GUIDELINES.
Post-test discussion
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.
http://www.bhiva.org/documents/Guidelines/Testing/GlinesHIVTest08.pdf
Post-test discussion
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.
http://www.bhiva.org/documents/Guidelines/Testing/GlinesHIVTest08.pdf
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