False Positive STD Test: Causes and What to Do Next

Yes — a false-positive STD/STI result can happen, but it is uncommon with modern laboratory testing and it is not equally likely across every infection or test type. Many STI results start as a reactive screening result, which may need additional or confirmatory testing before it is considered a final answer. An unexpected positive should never simply be dismissed, and feeling healthy does not prove a result is wrong. Only a qualified healthcare professional can interpret your specific result.

Many STIs can be present without noticeable symptoms. Having no symptoms — and feeling completely well — does not mean an unexpected positive result is automatically a false positive. That is one of the main reasons screening exists at all.

Unexpected positive result? Start here.

1. Don't assume it is false. A reactive result is a real finding that needs review.
2. Check what was tested. Note which infection was flagged and which method was used (antibody test, antigen test, or NAAT).
3. Remember that many STIs cause no symptoms. Absence of symptoms is not evidence against a result.
4. Ask a qualified healthcare professional whether confirmation, additional testing, or repeat testing is appropriate for your situation.
5. Expect different pathways. Follow-up differs by infection and by test — there is no single universal next step.

Whether repeat or confirmatory testing is appropriate depends on the infection, test type, and result.

This page explains what a false positive is, why screening tests are designed to occasionally produce one, and why confirmatory testing exists. It does not interpret your personal result.

What is a false positive STD test?

A false positive STD test is a result that indicates an infection when the person does not actually have that infection. It is the opposite of a false negative, which misses an infection that is truly present.

Many sexually transmitted infections are evaluated in stages: an initial screening test, followed by additional or more specific testing when the screen is reactive. The U.S. Centers for Disease Control and Prevention publishes recommended testing and diagnostic approaches for STIs specifically so that a single reactive screen is not treated as a final diagnosis on its own (per CDC).

False positive vs. false negative STD test

• False positive: the test indicates an infection when the person does not actually have that infection.
• False negative: the test does not detect an infection that is actually present.

Timing matters for the second one. Testing too soon after an exposure is a common reason people worry about false negatives, because different infections become detectable over different timeframes. If you are trying to work out whether you tested too early, see our guides to STI window periods and how long after exposure to get an STD test.

How common are false positives?

False positives are uncommon with modern laboratory-based STI testing, but they are not zero. How often they occur depends on:

• the specific infection being tested for
• the laboratory method used (antibody test, antigen test, nucleic acid amplification test, etc.)
• the population being screened
• whether additional or confirmatory testing is performed after a reactive screen

Because performance varies by test and by setting, it is not possible to give a single "false positive rate" that applies to every STD test. Recommended testing approaches are built in stages so that the final reported diagnosis reflects the whole evaluation, not the screen alone.

Can a chlamydia or gonorrhea test be a false positive?

Chlamydia and gonorrhea are usually tested with nucleic acid amplification tests (NAATs), which the CDC describes as the most sensitive and specific tests available for these infections (per CDC). Because their specificity is high, a false-positive result is uncommon — but "uncommon" is not the same as impossible, and no laboratory test is perfect.

A few medically supportable points about how an unexpected positive can arise:

• Specificity is very high, not absolute. Even a highly specific test will occasionally flag someone who does not have the infection.
• Screening in low-prevalence groups. When any test is used in a population where the infection is rare, a larger share of the positive results will be false positives, purely as a statistical property of screening (per USPSTF). This is not a defect in the test.
• Specimen and processing factors. Specimen type, collection, and handling affect NAAT performance, which is why the CDC specifies which specimen types are recommended for each test (per CDC).
• Repeat or additional testing is a clinical decision. Whether it applies to you is a judgment for a qualified clinician — it is not a universal requirement after every positive result.

If you would like to know what an in-person visit involves before any repeat testing, see what to expect at a Labcorp STI visit.

Why do false positives happen?

A false positive can happen for several reasons. None of them mean the laboratory was careless.

• Cross-reactivity. Some antibody-based tests can react to antibodies produced against something other than the target infection — for example, another related pathogen, a recent vaccination, or an autoimmune condition (per MedlinePlus).
• Biologic false-positive reactions on non-treponemal syphilis tests. This is a specific, well-described situation: non-treponemal syphilis tests (such as RPR or VDRL) can occasionally be reactive in people without syphilis, which is one reason syphilis is not diagnosed on a single test result. This mechanism is specific to non-treponemal syphilis testing — it is not a general explanation for an unexpected HIV, hepatitis, herpes, or NAAT-based result.
• Antibodies that persist after a past infection. Some tests detect antibodies rather than the organism itself, and those antibodies can remain detectable long after an infection was treated. This is why the test type matters so much when interpreting a result.
• Sample handling or lab variability. Any laboratory process has a small amount of built-in variability, which is one of the reasons additional testing exists.
• Low prevalence in the population being tested. Even a very accurate test will produce more false positives, in relative terms, when it is used in a population where the infection is rare. This is a well-known property of screening tests (per USPSTF) and is not a flaw in the test itself.

Why screening tests are designed this way

Screening tests are intentionally tuned to be sensitive — meaning they are designed to catch as many true infections as possible, even at the cost of occasionally flagging a result that later does not confirm. Missing a true infection (a false negative) can have serious consequences, so screening tests err on the side of catching too much rather than too little.

Confirmatory and supplemental tests are tuned differently. They are designed to be specific — meaning they are much less likely to react to anything other than the target infection. Running a sensitive screen first and a more specific test second is a deliberate design choice, not a sign that the first test failed.

In plain English:

• Sensitivity = the test's ability to correctly flag people who truly have the infection.
• Specificity = the test's ability to correctly clear people who truly do not have the infection.
• Screening = a first-line, sensitive test used broadly.
• Confirmatory or supplemental testing = further testing used to clarify a reactive screen before a diagnosis is made.

Why confirmatory testing matters

Confirmatory testing is the reason a reactive screening result is not the same thing as a diagnosis. A licensed clinician looks at the screening result together with any further testing (and often the person's history, symptoms, and risk factors) before deciding what the result actually means.

For several infections — HIV and syphilis among them — recommended approaches include specific supplemental steps after a reactive screen (per CDC). This is standard practice, not a special extra step reserved for unusual cases.

For HIV, syphilis, and hepatitis B, when the applicable laboratory workflow calls for reflex confirmation, the laboratory may perform that confirmatory step automatically and include it with the reported result. Confirmation workflows are not the same for every infection, and an unexpected result does not automatically mean you need to order another test yourself. LabTestsOnDemand does not diagnose or treat any condition.

How this differs by infection and test type

In principle any laboratory test can be wrong. In practice, the likelihood and the mechanism differ by infection and by assay.

HIV

HIV testing is performed in stages. A reactive initial screening test — often a laboratory antigen/antibody test — is not by itself equivalent to a confirmed HIV diagnosis; supplemental testing is used to determine what a reactive screen means (per CDC). Point-of-care and laboratory tests behave differently, and the follow-up depends on which test was used. A reactive HIV screen should be reviewed promptly with a qualified healthcare professional rather than self-interpreted in either direction.

Syphilis

Syphilis testing uses two different categories of test, and the distinction matters:

• Treponemal tests (such as TP-PA, EIA, or CIA) detect antibodies against the organism itself and can remain reactive after an infection has been treated, which is why a reactive treponemal test is interpreted alongside the rest of the testing algorithm.
• Non-treponemal tests (RPR, VDRL) are reported as titers and are interpreted differently. Titers generally change with disease activity and treatment, which is why they are commonly used for follow-up (per CDC).

Because of this, an unexpected syphilis result cannot be interpreted without knowing which test was reactive and where it sits in the overall testing algorithm. Do not attempt to interpret your own titer — that requires a clinician who can see the full sequence of results and your history.

Herpes (HSV-1 and HSV-2)

Herpes testing is not one test. Lesion-based testing (NAAT or culture from a sore) tests for the virus itself when a lesion is present. Type-specific antibody (IgG) testing tests the blood for antibodies and does not require a lesion — this is the type included in blood panels such as our Comprehensive Sexual Health Panel.

Type-specific HSV antibody testing can sometimes produce unexpected results, and low-positive HSV-2 IgG results in particular can be harder to interpret. CDC guidance discusses confirming certain low-positive HSV-2 serologic results with a different assay before the result is accepted (per CDC). Interpretation depends on the specific test used, the reported value, and your clinical context.

Two important limits: HSV antibody testing cannot tell you when you acquired the infection or from whom, and a positive result should not be judged false by the person who received it. That determination belongs to a clinician.

Chlamydia and gonorrhea

These are typically tested with NAATs, which are highly sensitive and specific (per CDC). False positives are uncommon, and any unexpected result is addressed clinically rather than by repeating the test on your own.

Trichomoniasis

Trichomoniasis — also included in our Comprehensive Sexual Health Panel — is most often tested with a NAAT, which the CDC describes as the most sensitive method for detecting it (per CDC). Older laboratory methods are less sensitive than NAAT. Because assays differ in performance and in the specimen types they are validated for, an unexpected trichomoniasis result should be interpreted according to the actual assay used and your clinical context.

Hepatitis C

A reactive hepatitis C antibody result does not by itself establish current infection: antibodies can persist after an infection that has cleared or been cured. CDC guidance describes HCV RNA testing as the step used to determine whether there is current infection (per CDC). So a reactive HCV antibody result is a signal to test further, not a finished answer. Our panels use hepatitis C antibody testing; HCV RNA testing is a separate test and is not included in our STI panels.

Hepatitis B

Hepatitis B testing works differently from hepatitis C and should not be described as the same screen-then-confirm pathway. Hepatitis B is usually interpreted using a combination of markers — commonly hepatitis B surface antigen (HBsAg), antibody to surface antigen (anti-HBs), and antibody to core antigen (anti-HBc) — because different patterns reflect very different situations, including current infection, past resolved infection, and vaccination-related immunity (per CDC). What an unexpected hepatitis B result means therefore depends on which marker is positive or reactive. This is not something to work out from a panel on your own. LabTestsOnDemand's STI panels include hepatitis B surface antigen testing; other hepatitis B markers are ordered separately by a clinician.

"I was treated, but my test is still positive"

This is a common and understandable worry, and the answer depends on the infection and the test.

For some infections, a test can remain positive for a period after treatment, which is why retesting timing is a clinician decision. It also helps to know that a test of cure and a test of reinfection are different things: the appropriate timing depends on the infection and the test used, and the right interval should be determined with a qualified healthcare professional. This does not apply uniformly to every infection or every test method.

Separately, some antibody tests can stay reactive after a past infection because they detect the immune response rather than the organism.

Because the timing and reasoning differ by infection, do not set your own retesting schedule. Ask the clinician managing your care what applies to your infection and your test.

What should you do after an unexpected positive result?

1. Do not dismiss the result because you feel fine. Many STIs can be present without symptoms, so having no symptoms is not evidence that a positive result is false.
2. Review the result carefully. Note which infection was flagged, which test method was used, and whether the report describes the result as reactive, positive, or preliminary.
3. Discuss the result with a qualified healthcare professional. They can interpret the result alongside your history, symptoms, and any recent exposures — something no article can do for you.
4. Ask whether additional or repeat testing is appropriate. For some tests and situations further testing is standard; for others it is not. That call belongs to your clinician.
5. Follow the next steps your provider recommends. Do not self-diagnose based on general information.

For a fuller walkthrough of what happens after a positive result, see what to do after a positive STD test. Related reading: how to read STD test results.

A note on how our testing works

LabTestsOnDemand offers physician-authorized STI panels drawn in person at a Labcorp facility, not at-home kits. Our Standard STI Panel includes six tests (HIV, syphilis, hepatitis B, hepatitis C, chlamydia, and gonorrhea), and our Comprehensive Sexual Health Panel adds HSV-1, HSV-2, and trichomoniasis. LabTestsOnDemand does not diagnose or treat any condition. Qualified healthcare professionals interpret your results and determine whether additional or confirmatory testing is appropriate.

Ordering another panel is not automatically the right response to an unexpected positive result. Whether repeat or confirmatory testing is appropriate — and which test to use — depends on the infection, the test type, and the result, so speak with a qualified healthcare professional first.

If you want to schedule private, in-person STI testing, you can start a Standard STI Panel order. For general information about confidential STI testing options, see our overview of confidential STD testing.

Sources

• Centers for Disease Control and Prevention. Sexually Transmitted Infections Treatment Guidelines, 2021. https://www.cdc.gov/std/treatment-guidelines/
• Centers for Disease Control and Prevention. Chlamydial Infections — STI Treatment Guidelines. https://www.cdc.gov/std/treatment-guidelines/chlamydia.htm
• Centers for Disease Control and Prevention. Gonococcal Infections Among Adolescents and Adults — STI Treatment Guidelines. https://www.cdc.gov/std/treatment-guidelines/gonorrhea-adults.htm
• Centers for Disease Control and Prevention. Trichomoniasis — STI Treatment Guidelines. https://www.cdc.gov/std/treatment-guidelines/trichomoniasis.htm
• Centers for Disease Control and Prevention. Genital Herpes — STI Treatment Guidelines (type-specific serologic testing). https://www.cdc.gov/std/treatment-guidelines/herpes.htm
• Centers for Disease Control and Prevention. Syphilis — STI Treatment Guidelines (treponemal and non-treponemal testing). https://www.cdc.gov/std/treatment-guidelines/syphilis.htm
• Centers for Disease Control and Prevention. HIV — STI Treatment Guidelines. https://www.cdc.gov/std/treatment-guidelines/hiv.htm
• Centers for Disease Control and Prevention. Getting Tested for HIV. https://www.cdc.gov/hiv/testing/
• Centers for Disease Control and Prevention. Clinical Testing and Diagnosis for Hepatitis B. https://www.cdc.gov/hepatitis-b/hcp/diagnosis-testing/index.html
• Centers for Disease Control and Prevention. Clinical Screening and Diagnosis for Hepatitis C. https://www.cdc.gov/hepatitis-c/hcp/diagnosis-testing/index.html
• U.S. Preventive Services Task Force. Screening for Chlamydia and Gonorrhea: Recommendation Statement. https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/chlamydia-and-gonorrhea-screening
• MedlinePlus (U.S. National Library of Medicine). How to Understand Your Lab Results. https://medlineplus.gov/lab-tests/how-to-understand-your-lab-results/