Syphilis is a bacterial infection caused by the organism Treponema pallidum that is commonly transmitted through sexual contact. The infection often presents with mild or absent symptoms in its early stages, making testing the only reliable method for detection. If left untreated, syphilis can progress through several stages and cause serious, long-term health complications affecting the brain, nerves, and heart. Timely testing and diagnosis are important for receiving treatment and preventing further transmission of the infection.
Finding a Testing Location
A variety of locations offer confidential syphilis testing, with options varying based on cost, privacy preferences, and convenience. Public health clinics and local health departments are often highly accessible, frequently providing low-cost or free testing services for sexually transmitted infections, including syphilis. These facilities typically prioritize patient confidentiality and may offer walk-in appointments or same-day service.
Many people choose to get tested as part of their routine healthcare with a primary care physician or OB-GYN. Testing can be integrated into an annual physical or check-up, offering a familiar and comfortable setting. Urgent care centers and walk-in clinics also provide syphilis testing, which can be a good option for those needing immediate attention or who cannot wait for a scheduled appointment.
For those seeking maximum privacy, online services and at-home collection kits are available, allowing a sample to be collected at home and mailed to a laboratory for analysis. Even with at-home kits, the sample is processed by a certified laboratory, and any positive result requires follow-up with a healthcare provider for diagnosis and treatment. Most testing options use a simple blood draw to obtain the necessary sample for serological testing.
The Different Types of Syphilis Tests
Syphilis diagnosis relies on a two-step serological testing protocol because a single test alone is not sufficient for a definitive conclusion. These tests detect antibodies produced by the body in response to the infection, rather than the bacteria itself. Testing is generally categorized into two groups: non-treponemal and treponemal tests.
Non-treponemal tests, such as the Rapid Plasma Reagin (RPR) and Venereal Disease Research Laboratory (VDRL), are typically used for initial screening. These tests look for antibodies that are not specific to the syphilis-causing bacteria but are produced in response to the cellular damage caused by the infection. Results from these screening tests are reported as a quantitative titer, such as 1:8 or 1:16, which indicates the concentration of antibodies present in the blood.
The non-treponemal test titer often correlates with disease activity and is used to monitor a patient’s response to treatment. These tests can sometimes yield a false positive result due to other medical conditions, such as autoimmune diseases, pregnancy, or other acute infections. Therefore, a positive screening test must be confirmed by a second, more specific test.
Treponemal tests, including the Treponema pallidum Particle Agglutination (TP-PA) or Fluorescent Treponemal Antibody Absorption (FTA-ABS), are confirmatory tests that detect antibodies specific to the Treponema pallidum bacterium. These specific antibodies usually appear earlier in the course of infection than the non-treponemal antibodies. Once an individual is infected, these antibodies generally remain detectable for life, even after successful treatment.
Testing is usually done using a blood sample, though a sore or lesion can sometimes be swabbed for direct detection methods like PCR in early stages. Modern laboratories may use a “reverse algorithm,” beginning screening with a treponemal test and then using a non-treponemal test for confirmation and to monitor disease activity. Both the traditional and reverse algorithms require both types of tests to establish a confirmed diagnosis.
Interpreting Your Results
Interpreting the combination of treponemal and non-treponemal test results determines the final diagnosis and necessary next steps. A negative result on both types of tests means that no infection was detected, and a person is unlikely to have syphilis. If there is a high clinical suspicion of very early infection, when the body has not yet produced enough antibodies, repeat testing within a few weeks may be recommended.
A diagnosis of current or past syphilis is strongly indicated when both the non-treponemal (RPR/VDRL) and treponemal (TP-PA/FTA-ABS) tests are reactive, or positive. If the RPR test is reactive, it typically suggests an active infection, and the titer helps determine the severity or stage of the disease. Conversely, if the treponemal test is positive but the non-treponemal test is negative, it often means the person had syphilis in the past and was successfully treated.
In cases where a non-treponemal test is positive but the treponemal test is negative, the non-treponemal result is likely a biological false positive caused by another condition. After a positive diagnosis is confirmed, treatment with antibiotics, typically penicillin, is administered, and the quantitative non-treponemal titer is monitored over time to ensure the treatment is effective. Partner notification is also important to ensure any sexual partners are informed and receive testing and treatment.