Routine serologic screening of patients at risk for HIV-1 or HIV-2 infection usually begins with a HIV-1/-2 antigen and/or antibody screening test, Antibodies against HIV-1 and HIV-2 are usually not detectable until 6 to 12 weeks following exposure and are almost always detectable by 12 months. They may fall to undetectable levels (ie, seroreversion) in the terminal stage of AIDS when the patients immune system is severely depressed.HIV virus causes Acquired Immunodeficiency Syndrome (AIDS). EIA is a screening test for HIV infection with a sensitivity of >99.9%. As per NACO guidelines, all reactive samples are tested by three different methods prior to release of report.