Blood test is a sure way to check for sexually transmitted diseases such as HIV and syphilis. Syphilis is a serious infection. It is passed from one person to another during sex. You could get syphilis by touching the blood or sores of a person who has syphilis, especially sores on the person's mouth, penis, vagina or anus. After many years, people with syphilis who don't get treatment may begin to have problems in their brain and spinal cord. Syphilis may damage the heart and other organs, too. If you have a syphilis sore, it's easier for HIV infection to get into your body through the sore. If you have syphilis, you should be tested for HIV. Blood tests are used to determine if one or both of the marrying couple had a disease that may be passed on to each other and it's also important to prevent the partner from getting the disease.