After 20 years of high-risk sexual behavior, TPAb negative can rule out the possibility of syphilis infection. TPAb is syphilis-specific antibody, which is a kind of protective antibody produced by the body after infection with syphilis spirochete. After the incubation period, if the indicator is negative, it means that the body has not been infected with syphilis. If you have been infected with syphilis in the past, even if you have been cured, the TPAb in your body will remain positive. There is an incubation period between the entry of syphilis spirochetes into the human body and the appearance of clinical symptoms, approximately 2-4 weeks. Generally speaking, after 6 weeks of high-risk sexual behavior, if a patient is infected with syphilis spirochetes, he or she can be screened out through the detection of TPAb. Since high-risk sexual behavior has been more than 20 years, as long as the blood test is negative for TPAb, the possibility of syphilis infection can be ruled out. If syphilis infection is suspected, it is important to seek medical attention and follow the doctor’s instructions for tests to clarify the diagnosis.