Getting an STD test done is important from multiple aspects. An STD like HIV is highly infectious and if not treated on time, it can progress into AIDS. Another problem with HIV is that sometimes the infected person may not show any symptoms and unknowingly, he or she may go on spreading the disease among other people, sexually and otherwise. The human immunodeficiency virus destroys the CD4+ cells. These are part of the immune system and a type of white blood cells. These cells are also called T cells. They protect your body against infection. When their number dwindles, your body becomes vulnerable to even casual bacteria and viruses floating in the air.