In this guide
Key takeaways
- "Detected," "reactive" and "positive" generally mean the test found what it was looking for. "Not detected," "nonreactive" and "negative" mean it didn't, at the time of testing.
- A negative result taken during the window period may not be final. CDC advises retesting after the window period for the type of HIV test you took.
- Some results are screening steps, not diagnoses. Positive HIV antibody tests, syphilis tests and hepatitis C antibody tests each need a follow-up test.
- Syphilis antibody tests often stay reactive for life after treatment, so an old, treated infection can still show up as reactive.
- After treatment for chlamydia, CDC says not to retest with a NAAT less than 4 weeks after therapy, because leftover genetic material can cause a false positive.
Getting STI results back can be stressful, and the report doesn't always help. One line says "nonreactive," another says "not detected," and a syphilis result might show something like "reactive, titer 1:4." It's easy to panic over a word you don't recognize, or to feel relieved by a result that actually means "test again later." This guide walks through the vocabulary, then explains how to read the results for the infections people test for most often. It's general information to help you understand your report and have a better conversation with your clinician, not a replacement for one. If you just received a positive result from a home kit, our guide to next steps after a positive at-home test is a good companion to this one.
The words you'll see on a results report
Different labs use different wording for the same idea. Here's a decoder.
| You might see | What it generally means |
|---|---|
| Negative, Not detected, Nonreactive | The test didn't find the infection, its genetic material, or antibodies to it in this sample at this time. |
| Positive, Detected, Reactive | The test found what it looks for. For some tests that's a diagnosis; for others it's a signal that needs a second test. |
| Preliminary positive | A first-step result that needs a confirmatory test before it's considered a diagnosis. |
| Indeterminate, Equivocal, Inconclusive | The result didn't clearly land on either side. Usually means repeat or additional testing. |
| Invalid, Unable to report | The test didn't work on this sample, for example because the sample was too small, leaked or arrived too late. You'll need a new sample. |
| Titer (such as 1:8) | How much a sample can be diluted and still react. Used for syphilis tests to track activity and treatment response. |
| Reflex test | A follow-up test the lab runs automatically on the same sample when the first result is positive. |
Also check which body site each result refers to. A "not detected" chlamydia result from a urine sample tells you nothing about the throat or rectum. Our guide to chlamydia and gonorrhea sample types explains why this matters.
Chlamydia, gonorrhea and trichomoniasis
These are usually tested with a nucleic acid amplification test (NAAT), which looks for the organism's genetic material in urine or a swab. Results are typically reported as detected or not detected for each infection and site.
- Detected: You have the infection at that site. These infections are typically treatable with antibiotics, and partners need to be told so they can be tested and treated. See how to tell a partner.
- Not detected: No infection was found at that site at the time of testing. If the test was very soon after an exposure, ask whether a repeat test makes sense. Our window periods guide has the timing.
Retesting after treatment follows specific rules in CDC's guidelines:
| Situation | What CDC recommends |
|---|---|
| Treated for chlamydia or gonorrhea | Retest about 3 months after treatment, whether or not you believe your partners were treated, to check for reinfection. |
| Retesting too early after chlamydia treatment | NAATs should not be used less than 4 weeks after therapy, because nonviable organisms can still be detected and cause a false positive. |
| Pregnant and treated for chlamydia | A test of cure about 4 weeks after treatment. |
| Treated for gonorrhea in the throat | A test of cure 7 to 14 days after treatment. |
For more on test of cure vs reinfection checks, see retesting after STI treatment.
HIV results
HIV test results depend heavily on which test you took and when. CDC describes how soon each type can usually detect HIV after an exposure:
| Test type | Can usually detect HIV |
|---|---|
| Nucleic acid test (NAT) | 10 to 33 days after exposure |
| Lab antigen/antibody test (blood from a vein) | 18 to 45 days after exposure |
| Rapid antigen/antibody test (finger stick) | 18 to 90 days after exposure |
| Antibody test, including most rapid tests and self-tests | 23 to 90 days after exposure |
- Negative or nonreactive: If your test was taken inside the window for that test type, CDC advises testing again after the window period. If you aren't sure which test you had, ask the testing service or clinic.
- Reactive or preliminary positive: CDC says a positive result on any antibody test needs a follow-up test to confirm it. A reactive self-test means getting follow-up testing from a health care provider. It doesn't mean you've been diagnosed yet.
If you had a possible HIV exposure in the last 72 hours, CDC says PEP must be started within that window. Contact a provider, urgent care or an emergency room right away. Testing can follow.
Our comparison of HIV test types and our guide to using an HIV self-test go deeper.
Syphilis results
Syphilis results confuse people more than any other, because diagnosis uses two different kinds of blood test, and one of them usually stays positive for life.
Nontreponemal (RPR or VDRL)
Reported with a titer, such as 1:16. Titers track how active the infection is and how well treatment is working.
Treponemal
Detects antibodies to the syphilis bacterium itself. Most people stay reactive for life, even after successful treatment.
CDC says both types are needed for a presumptive diagnosis. Using only one can miss early infection or lead to a false positive. Labs may run them in either order. In the "reverse sequence" approach, the lab screens with a treponemal test first, then automatically runs a nontreponemal test if that is reactive. If the two disagree, a second treponemal test settles it.
Reading a titer
A titer of 1:16 means the sample still reacted after being diluted 16 times. Higher numbers mean more antibody. After treatment, clinicians look for the titer to fall. CDC describes a meaningful change as fourfold, which is two dilution steps, such as going from 1:16 to 1:4. For a fair comparison, follow-up tests should use the same method, ideally at the same lab, because RPR and VDRL titers can't be compared directly.
Reactive, but treated years ago?
Because treponemal antibodies usually persist, a past, cured infection can show up as reactive. The FDA notes the same thing about the at-home syphilis antibody test: it can be positive in people who were treated in the past. Tell your clinician about any past diagnosis so they can interpret the full picture.
False positives
CDC lists several things that can cause a false-positive nontreponemal result, including other infections (HIV among them), autoimmune conditions, vaccinations, injection drug use, pregnancy and older age. That's one reason a single test isn't enough for a diagnosis.
Hepatitis C results
Hepatitis C testing usually happens in two steps. CDC recommends starting with an antibody test and, if it's reactive, automatically running an RNA test to check for current virus.
| Antibody | RNA | What it generally means |
|---|---|---|
| Nonreactive | Not usually needed | No hepatitis C infection, unless a possible exposure happened in the last 6 months, when CDC says RNA testing is still recommended. |
| Reactive | Not detected | No current infection. The antibodies suggest a past infection that has resolved. |
| Reactive | Detected | Current infection. Your clinician will talk with you about care and treatment. |
A reactive antibody result on its own doesn't prove you have hepatitis C now. Our hepatitis B and C testing guide covers both viruses.
Herpes blood tests
Herpes blood tests are reported differently from other STI tests and often aren't included in a standard panel automatically. CDC says type-specific herpes blood tests may be considered in some situations rather than for everyone. If you got a herpes result, especially a low positive, read our dedicated guide to herpes blood test results before drawing conclusions, and see whether your panel included herpes at all.
When to retest or ask for a second look
Any test can give a false result, and the FDA names false positives and false negatives as the main risks of the home STI tests it has authorized. Use this checklist to decide whether to follow up:
- Was the test taken inside the window period for that infection? If so, plan a repeat test.
- Do you still have symptoms despite a negative result? See negative test but still have symptoms.
- Was the result a screening step (HIV antibody, syphilis, hepatitis C antibody) that needs confirmation?
- Did the test cover every body site you use for sex?
- Were you treated in the last few months? Check the retest timing above before testing again.
- Was the result invalid or indeterminate? Collect a new sample or ask what additional test is needed.
For a deeper look at testing errors, see can STI tests be wrong?
Questions to ask about your results
- "Is this a final result or a screening result?"Find out whether a confirmatory test is needed and whether the lab already ran it.
- "Which body sites did this cover?"Make sure the test matched your exposures.
- "Was it too early to test?"Ask whether the timing could affect a negative result and when to repeat.
- "What's the treatment, and when do I retest?"Get the retest date on your calendar before you leave.
- "What should I tell my partners?"Ask whether the clinic or health department can help with partner notification, and whether your partners should be tested for anything else.
If you were diagnosed with one infection, CDC recommends testing for others too. Our guide to why one diagnosis means testing for others explains which ones.
Frequently asked questions
What does "nonreactive" mean on an STI test?
Nonreactive means the test didn't find antibodies or antigens it was looking for in your sample at the time it was taken. It's the same idea as negative. If the test was taken during the window period after an exposure, a repeat test may still be needed.
Is a reactive HIV test a diagnosis?
Not on its own. CDC says a positive result on any HIV antibody test, including a self-test, needs a follow-up test to confirm it. A health care provider can arrange confirmatory testing and, if HIV is confirmed, connect you with care.
Why is my syphilis test reactive if I was treated years ago?
Treponemal syphilis tests usually stay reactive for life, even after successful treatment, so a past infection can still show up. Clinicians use a second type of test, reported as a titer, to judge whether there's current activity. Tell your clinician about any past diagnosis and treatment.
Can I retest right after finishing chlamydia treatment?
CDC advises against using a NAAT less than 4 weeks after chlamydia treatment, because nonviable organisms can still be detected and cause a false positive. CDC recommends retesting about 3 months after treatment to check for reinfection, and a test of cure about 4 weeks after treatment during pregnancy.
What does a positive hepatitis C antibody test mean?
It means you've been exposed to hepatitis C at some point. It doesn't show whether the infection is current. An RNA test answers that: if RNA is not detected, the infection has resolved; if RNA is detected, you have a current infection and should talk with a clinician about treatment.
Ready to test, or retest?
Compare home kits and lab-based options by which infections and body sites they cover, and how results are delivered.
Compare testing options →Sources
- Getting Tested for HIV — Centers for Disease Control and Prevention
- Syphilis (STI Treatment Guidelines) — Centers for Disease Control and Prevention
- Chlamydial Infections (STI Treatment Guidelines) — Centers for Disease Control and Prevention
- Gonococcal Infections Among Adolescents and Adults (STI Treatment Guidelines) — Centers for Disease Control and Prevention
- Clinical Testing and Diagnosis for Hepatitis C — Centers for Disease Control and Prevention
- FDA Marketing Authorization Enables Increased Access to First Step of Syphilis Diagnosis — U.S. Food and Drug Administration
This article is for general information only and is not medical advice, diagnosis or treatment. Testing needs differ from person to person, so talk with a clinician, local health department or sexual health clinic about your situation. If you think you were exposed to HIV in the last 72 hours, seek care right away to ask about PEP. Guidance referenced here was checked against official sources in October 2026 and can change. Some links on this site are affiliate links, which means we may earn a commission if you buy through them, at no extra cost to you.