HIV – Understanding the Window Period
The HIV window period often is the cause of a lot of confusion.
There is a lot of information on the web throwing up numbers like 3 months, 6 months even 1 year. So what exactly if the HIV window period?
To better understand this, let us take a step back in time to when HIV was first discovered. At the same time, learn a little about how our immune system works.
The HIV virus was discovered in 1983. Prior to that, it was not known what was causing the disease known as AIDS that was ravaging certain communities in the world.
After scientists discovered the existence of the HIV virus, they had to find a way to determine if a person has this virus in his body or not.
The ELISA Test and Our Immune System
In 1985, they developed a test called ELISA which is based on a very basic principle of how our immune systems work.
When our body is attacked by a virus, it will produce anti-bodies to fight the virus. Anti-bodies are unique. The anti-bodies used to fight HIV would be completely different to the ones used to fight dengue, for example, or any other virus.
So finding HIV anti-bodies in the body is indirect evidence that there is HIV virus in the body too. The ELISA test does exactly that. It tests for the presence of HIV anti-bodies.Click here to learn about the Different Generations of ELISA
Imagine each virus infection is a fire that starts in the body. Each of these fires produces a uniquely colored smoke. When we see a particular colored smoke, we assume that there is that particular type of fire burning away. The ELISA tests for HIV colored smoke but does not detect the fire itself.
But there was one big problem. It sometimes takes the body a long time before the body produces enough anti-bodies to be detected by the ELISA test. In other words, the fire has to burn for a long time before it produces enough smoke that can be detected by ELISA.
This period when a person is infected with HIV and the ELISA test is unable to pick it up (the period when the fire is burning but there is no smoke) is called the window period.
This was correctly recognized to be a very important finding and rightly so because a person infected with HIV within the window period can get tested and be told he does NOT have HIV. He will then not take steps to protect himself and the people around him thus increasing the risk of spreading the disease.
Different Types of HIV TestsClick here for HIV Testing FAQ
Scientist has ever since been working on improving and coming up with new and better testing techniques and technology. There are now multiple different tests for HIV including ELISA, ECLIA, CMIA, Rapid Tests, Western Blot, RNA PCR, DNA PCR and P24 Combo Tests. There are also multiple different manufacturers of each test. All of these tests have their own rates of accuracy, window periods and applications in the management of HIV. To make things even more confusing, there are also tests for indirect evidence of HIV infection like CD4 cell count and CD4 CD8 cell ratio.
So when you read somewhere or someone tells you that the window period for HIV is X number of months, your next logical question should be ‘by using which test?’
To know which test done when has what accuracy requires a lot of professional knowledge. This information is also constantly changing as more and more research information is published. There are also other considerations such as waiting time, anonymity, costs etc
It is still best to speak to Our Doctors who are certified and trained in HIV counseling and testing to find out which test is most appropriate for you.Click here for Updates on the HIV testing Window Period
One thing remains constant. If you are at any risk of HIV at all, no matter how minute, you MUST get tested. But as for which test to do and when to test, it is still best to speak to a medical professional trained in HIV matters.Click here to see the full range of our HIV/STD Services
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If you had a high risk exposure to HIV within the past 72 hours, you can take medicines to reduce your risk of actually contracting HIV. Find out more on HIV PEP Treatment.
About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.