What is the long term accuracy of 4th generation HIv test say 2, 4, 6, 10, years after infection.

One hundred percent. The 4th generation HIV tests -- also called "duo" or "combo" test because they include two tests in one: HIV antibody and p24 antigen, a protein in the outer coat of the virus. These tests become positive within 4 weeks of a new infection. Once positive, they remain positive for life. There are no exceptions.