STI test results: chlamydia, gonorrhea and syphilis
Chlamydia and gonorrhea are usually tested together on one urine sample or swab, and a positive result means the infection was found. Syphilis is a blood test read in two steps, because the first antibody test can be positive for other reasons. A negative result soon after an exposure may need repeating. Your doctor decides what your results mean for you. (CDC, 2021) (MedlinePlus, 2024) (MedlinePlus, 2025)
Chlamydia and gonorrhea
The recommended test is a nucleic acid amplification test (NAAT), which looks for the bacteria's genetic material. It can use first-catch urine, or a vaginal swab that you can collect yourself in the clinic; self-collected vaginal swabs work as well as ones a clinician collects. Rectal and throat swabs can also be tested. (CDC, 2021)
- Negative: no infection was found when the sample was taken. It can take weeks after infection for a gonorrhea test to turn positive, so a test soon after an exposure may need repeating. (MedlinePlus, 2024) (MedlinePlus, 2025)
- Positive: the infection was found. It needs treatment, and your sex partners need to know so they can be tested and treated if necessary. (MedlinePlus, 2024) (MedlinePlus, 2025) The CDC says a person diagnosed with chlamydia should also be tested for HIV, gonorrhea and syphilis. (CDC, 2021)
Retesting after a positive result
- About 3 months after treatment: the CDC says men and women treated for chlamydia or gonorrhea should be retested then, whether or not they think their partners were treated, because most repeat infections come from a partner who was not treated or a new partner. If 3 months is not possible, retest at the next visit within 12 months. (CDC, 2021)
- Not too soon: a chlamydia NAAT less than 4 weeks after finishing treatment is not recommended, because leftover dead bacteria can give a false positive. A routine "test of cure" is not needed for most people outside pregnancy. (CDC, 2021)
- Gonorrhea in the throat: the CDC asks for a test of cure 7 to 14 days after treatment. (CDC, 2021)
Partners
For both infections, the CDC says sex partners from the 60 days before your symptoms or diagnosis should be referred for testing and treatment; if the last partner was longer ago, that most recent partner should still be checked. (CDC, 2021)
Syphilis: why two tests
Syphilis tests look for antibodies in your blood. There are two kinds, and the CDC says they should be used together when the first one is reactive, because one reactive result alone can misclassify your status. (CDC, 2024) (MedlinePlus, 2025)
| Test type | What it finds | What it is used for |
|---|---|---|
| Nontreponemal (RPR or VDRL) | Antibodies that rise with active infection but can also come from other conditions | Reported as a titer; used to follow the infection over time (CDC, 2024) |
| Treponemal (for example TP-PA, FTA-ABS, EIA or CIA) | Antibodies made only against the syphilis bacterium | Usually stays positive for life, even after treatment, so it cannot show a new infection in someone treated before (CDC, 2024) |
- Which comes first depends on the lab. In the traditional order, a nontreponemal test is done first and a reactive one is confirmed with a treponemal test. In the reverse order, an automated treponemal test is done first, then a nontreponemal test, and a third treponemal test settles results that disagree. The CDC accepts both. (CDC, 2024)
- Reactive RPR, negative treponemal test: a "biologic false positive", caused by conditions other than syphilis. The CDC estimates it happens in 0.2% to 0.8% of people. (CDC, 2024)
- Both positive: you either have syphilis now or had it and were treated. Your provider uses your history to tell which. (MedlinePlus, 2025)
- Negative soon after an exposure: antibodies can take a couple of weeks to develop, so you may need another test. (MedlinePlus, 2025)
Titers in plain words
An RPR or VDRL result is reported as a titer, such as 1:4 or 1:32: the highest dilution of your blood that still reacts. A bigger second number means more antibody. (CDC, 2024)
- Only a fourfold change counts. A change of 4 times or more (such as 1:32 to 1:8) between two results on the same type of test is considered meaningful. RPR and VDRL titers cannot be compared with each other. (CDC, 2024)
- After treatment, titers usually fall at least fourfold within 12 months. In some people they fall less, or stay low but reactive for a long time (called "serofast"). (CDC, 2024)
- After past syphilis, the treponemal test usually stays positive, so a new infection is judged by the nontreponemal titer together with your history and an exam. (CDC, 2024)
Your doctor decides what your titer means and what happens next. This page does not give treatment advice. See also after an abnormal screening result.
Who should be screened
- Chlamydia and gonorrhea: the USPSTF recommends screening all sexually active women 24 or younger, and women 25 or older at increased risk (grade B, 2021). For men the evidence is insufficient (I statement). (USPSTF, 2021)
- Syphilis: the USPSTF recommends screening adolescents and adults at increased risk (grade A, 2022), and screening in pregnancy is covered on the syphilis screening page. (USPSTF, 2022)
The CDC's guidelines add more groups and how often to test. Full side-by-side details: sexual health screenings by age and chlamydia and gonorrhea screening.
Cost and coverage
Medicare Part B covers one screening for chlamydia, gonorrhea, syphilis and hepatitis B every 12 months, or at certain times in pregnancy, if you are pregnant or at increased risk and your provider orders it. You pay nothing if your primary care provider accepts assignment. (Medicare.gov) For private plans, see preventive screenings covered by insurance.
Questions people ask
What does a positive chlamydia or gonorrhea test mean?
It means the infection was found in your sample. MedlinePlus says you will need treatment, should tell your sex partners so they can be tested and treated if needed, and should be retested about 3 months after treatment because repeat infections are common. (MedlinePlus, 2024) (MedlinePlus, 2025)
Can a negative gonorrhea test be wrong?
MedlinePlus says a negative result does not rule out gonorrhea: it can take weeks after infection before a test turns positive, so the test may have been too soon after exposure. Ask your provider when to test again. (MedlinePlus, 2025)
Why do I need a second syphilis test?
No single blood test can tell for sure. The CDC says two kinds of antibody test should be used together when the first is reactive: a nontreponemal test (RPR or VDRL) and a treponemal test. Relying on one reactive result can misclassify your status. (CDC, 2024) (MedlinePlus, 2025)
What does an RPR titer of 1:8 mean?
A titer is the highest dilution of your blood that still reacts, so 1:8 is higher than 1:4. Its meaning depends on your history and stage, which your provider reads with it. The CDC says only a fourfold change, such as 1:32 to 1:8, between two results on the same type of test counts as a real change. (CDC, 2024)
Does Medicare cover STI testing?
Medicare Part B covers one screening for chlamydia, gonorrhea, syphilis and hepatitis B every 12 months, or at certain times in pregnancy, if you are pregnant or at increased risk and your provider orders it. You pay nothing if your primary care provider accepts assignment. (Medicare.gov)