variability of hiv virus

hi doc!
i got tested in a lab for hiv 6 months after my unprotected sex with a girl and had negative result each time. later i got the manual for the elisa test kit used in the lab, in which it said that "there may be false negative result due to the variability of the virus".
i am unable to understand.
please help me understand it doc, because its really disturbing.
thanks

[meworried]

Your test is 100% reliable and you should get out of all worries. A six month ELISA is more than accurate. False negative is a term used when ELISA is done withing window period (less than 6 weeks) and detectable amount of antibodies are not formed yet. Otherwise ELISA is very highly accurate and reliable.... Congrateulations that you are safe,,,,,,,,,,,, But never try any other unprotected "endeavor" in future. Sometime you don't get a second chance.

[regularjoey]

That's just CYA language, in case somebody thinks about a lawsuit.
An HIV test does not get approved by the FDA unless it is demonstrated that it is capable of detecting all known subtypes of HIV.

[bof]

thnks a lot friends

[bof]

what about new subtypes? how are they detected?

[regularjoey]

Sometimes people perform genetic sequencing of virus isolated from newly diagnosed persons.  If the sequence looks like a new "branch" on the HIV "family tree", it is designated as a separate subtype.  I don't remember the last time a new subtype was discovered, this was years ago.