How soon can I get tested for HIV?

No offense but that was pretty dumb. Sharing needles is the number one cause of HIV in the United States. If you go to the ER immediately and tell them what happened they can give you something to stop you from getting HIV at all. But there is a time frame. So I suggest you do it! If not then HIV can take 3months to a year to show up on the ELISA (HIV) test. If you are worried then do the right thing and go to the emergency room and get help.