Mar 04, 2010
What's the best HIV Test?
The best HIV test is one that provides you with an accurate and reassuring result in a time frame that suits you best. Everybody will have a different "best HIV test" because their circumstances will be slightly different. The main things to think about are firstly when you were possibly exposed to HIV and secondly how desperately you need to know the answer. The exposure time is important because it allows us to calculate the HIV window period, which is the time from HIV infection to detection.
There is a great deal of confusion regarding HIV testing which results mainly from the enormous leaps in our knowledge about HIV in the time since the epidemic began and the advancement of the technology behind the testing devices.Consequently the question as to which is the best HIV test depends very much on the individual circumstances.
We now have HIV testing methods that will allow us to identify HIV infection very early on indeed. This is important for all sorts of reasons, not least the fact that we know that the key period for passing HIV on to another person is in the first few months after infection, when the amount of virus in the infected person's blood stream, semen or vaginal fluids is likely to be very high. The amount of HIV virus in a body fluid is referred to as HIV viral load and in the early stages is likely to be many hundreds of thousands or millions of copies of virus in each one millitre of blood or fluid.
As the infection proceeds and the newly infected person's body gets a hold on the new HIV infection, the amount of virus falls and that person becomes, we think, much less infectious. So for example, if I were to become HIV positive today, then in around 2 weeks or so my viral load - the amount of virus in each 1ml of my blood or semen - would be rapidly increasing and starting to run into the millions of copies. I would be very infectious to those I had unprotected sex with.
Testing newly infected HIV positive people early allows us lots of opportunities to influence the outcome for the good. We know from studies that most people who are aware they are HIV positive are keen to avoid passing HIV on to others. They certainly do not want a moment of madness on their part to result in their loved ones becoming HIV positive too.
So, what is the best HIV test?
- Testing for HIV 7 days after exposure
Preliminary diagnosis of very early HIV and Hepatitis C disease is now possible at
7 days post possible exposure. This time frame was previously unavailable but utilisation of standard routine technology in a novel diagnostic style will facilitate very early diagnosis. The technique has had most application so far in terms of screening the human blood supply from blood donors and has reduced the numbers of inadvertent contamination with HIV and Hepatitis C virus very considerably. The technique is also employed in organ donation settings where organs to be donated are screened for the HIV-1, HIV-2,Hepatitis C and Hepatitis B viruses.
Thinking laterally and working with The Doctors Laboratory ( a major global referral laboratory in London and CPA, UKNEQUAS, WEQAS, ISFG and EMON approved for quality, robustness and high standards), we have collaborated to apply the blood and tissue screening, ultra-high sensitive technique to beginning the diagnostic process for the
The ultra-fast diagnostic technique utilises a fully automated system made by Roche and the testing method
uses polymerase chain reaction (PCR) or NAT (Nucleic Acid Amplification) to
detect miniscule amounts of viral (and the technique can be applied to bacteria) genetic material.
The process works as follows. We take a measured amount of blood sufficient to run the three NAT tests for HIV-1 and HIV-2; Hepatitis C virus and Hepatitis B virus. We can also include syphilis IgG and IgM within that screen. The test is performed using the Roche platform and runs on the "sample in, results out" technique
which reduces chances of contamination of product etc to zero. Should a positive sample be produced the whole specimen is drilled down to identify the virus producing the positive result and further confirmatory tests are performed.
The outcome is a highly sensitive, highly accurate detection methodology for detection of the identifed viruses. The turnaround time is swift, taking a maximum of 4 days.
- HIV 1 and 2 antibodies and p24 antigen test (HIV DUO or HIV Combi test)
This HIV test is licensed in the EU for use after 28 days after a possible exposure. It is probably much better than this and will probably identify the majority of newly infected HIV positive individuals at between 14 and 21 days. This HIV test is referred to as a fourth generation HIV test. Certainly in our clinic we have had many new diagnoses of patients using this HIV DUO test combination in that time frame.
The HIV DUO test relies on the principle that when HIV first establishes itself in the body it will start to replicate rapidly and almost as a by-product of this replication a core protein - the HIV p24 antigen - is produced in huge amounts from around 10 days or so after first infection and before or during the time when antibodies to HIV are being formed. The p24 antigen will then stay at a very high level for the first few months after infection and later decline in line with the decline in HIV viral load as referred to above. It will though never completely disappear and will run a variable course of detection through the rest of the illness.
So in general, p24 antigen is formed slightly before antibodies are forming allowing us to close the gap between infection to detection time - the HIV window period. As time goes on, then the majority of newly infected HIV positive people will form antibodies to HIV 1 or 2 by 28 days. In combination then, looking for both the HIV 1 p24 antigen and also HIV 1 and 2 antibodies will allow for much earlier detection of HIV than looking for HIV antibodies alone.
- HIV 1 and 2 antibody test
This test is where the most confusion is centred around. When the epidemic began in the early 1980's our testing methods and devices were relatively poor and frequently produced false results. This was largely because researchers were scrambling to find firstly the cause and then a test for a new and virulent disease.
I remember those panic struck early days very well. The false results - both false negative and false positives led to great caution in terms of interpreting the HIV test results at that time. As time has passed, our understanding of the disease, it's cause, it's likely progress and also the testing methods have improved enormously.
We have moved from rudimentary tests in the early 1980's to modern, accurate, easy to use third and fourth generation HIV testing methods in 2010. HIV 1 and 2 antibody tests in use in the UK will be either third or fourth generation test. Modern third generation tests will identify well over 99% of newly infected HIV positive people at 6 weeks after exposure even though they are licensed for use after 12 weeks after a possible exposure.
The best HIV test is always going to be the one that suits your time frame and also need to know level or anxiety level the best. Always remember though that if you have a high risk exposure such as unprotected sex with someone who is known to be HIV positive, or a condom break with someone who is known to be HIV positive then don't wait to test but talk to a doctor about HIV Post Exposure Prophylaxis (PEP) as soon as possible, ideally within 36 to 72 hours after the event.