http://labtestsonline.org/understanding/conditions/std.html
American Association for Clinical Chemistry
There are more than 20 known sexually transmitted diseases (STDs). Some of them will cause symptoms that should be brought to the attention of your doctor immediately. However, others may be "silent" - a person could have the disease but might not notice any symptoms of the infection. This document lists the most common STDs, including gonorrhea, syphilis, genital herpes, and more.