When to start treatment for HIV
BMJ Group Medical Reference
Doctors usually advise that you should start treatment with antiretroviral drugs before your CD4 count drops to 350.   CD4 cells are part of your immune system, and how many you have (your CD4 count) is a sign of how healthy your immune system is.
Research shows that people are likely to live longer if they begin treatment before their CD4 count drops to 250. 
If your CD4 count is more than 350, your body is managing to control HIV pretty well on its own. So the drugs may do you more harm than good. They may cause side effects and you may get resistant to the drugs. This means that the drugs won't work later on when you really need them to work.  But doctors don't all agree about this. Some think it makes sense to start treatment before your count goes down to 350. 
If you wait until your CD4 count is much lower than 350 before you start taking antiretroviral drugs, the side effects of the drugs may be much worse. 
If your CD4 count is 350 or lower, then your HIV doctor will probably offer you treatment, but it is usually up to you to decide when you would like to start. You need to think about:
How fast your CD4 count has been falling. For example, if it is falling slowly, you may want to hold off treatment for the time being. If it is falling fast, you may feel it is best to start now
Your viral load
Whether you have another illness, such as hepatitis C, which can affect the progress of HIV. 
Your immune system is made up of the parts of your body that fight infection. When bacteria or viruses get into your body, it's your immune system that kills them. Antibodies and white blood cells are part of your immune system. They travel in your blood and attack bacteria, viruses and other things that could damage your body.
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