How to Read STD Test Results: Common Terms Explained

Understanding an STI or STD lab report can feel confusing. Words such as reactive, nonreactive, detected, equivocal, and reference range mean different things depending on the infection tested, the assay used, and the laboratory that ran the sample. This guide explains, in plain English, the terms and formatting you may see on a report — it is not an interpretation of any personal result.

Medical disclaimer: This article is for general education only. It does not diagnose, interpret, or treat any medical condition. Only the clinician who ordered your test, or another qualified healthcare professional, can interpret your specific result in the context of your history, symptoms, exposure timing, and any confirmatory testing.

Start with the test name and specimen type

Before reading a result, look at what was actually tested and how the sample was collected. STI panels can include several different assay types, and each behaves differently:

• Blood draw serology — often used for HIV, syphilis, hepatitis B, and hepatitis C (per CDC).
• Urine NAAT (nucleic acid amplification test) — commonly used to detect Chlamydia trachomatis and Neisseria gonorrhoeae DNA/RNA.
• Swab NAAT — vaginal, cervical, rectal, or pharyngeal swabs may be used depending on exposure site.
• Antigen/antibody combination tests — for example, HIV 4th-generation screening assays.
• Antibody-only tests — such as HSV type-specific IgG serology.
• Non-treponemal serology (RPR/VDRL) — used in syphilis screening algorithms (per CDC).

The test name on the report tells you which target and method were used. A "positive" HIV screening test and a "positive" chlamydia NAAT do not mean the same thing operationally — the follow-up steps are different (per CDC).

What positive, reactive, and detected may mean

These terms generally indicate that the assay found what it was looking for, but the exact meaning depends on the test:

• Positive is often used with NAAT-based tests (chlamydia, gonorrhea, trichomoniasis) to indicate the pathogen's genetic material was detected above the assay's threshold.
• Reactive is often used with antibody or antigen/antibody screening tests (HIV, hepatitis, syphilis). A reactive screening result may be preliminary and typically requires confirmatory testing before it is considered a confirmed infection (per CDC).
• Detected is common on molecular reports and generally means the target nucleic acid was present at or above the limit of detection.

A reactive screening result is not automatically a confirmed diagnosis. For HIV, for example, a reactive 4th-generation screen is followed by an HIV-1/HIV-2 antibody differentiation immunoassay, and sometimes an HIV-1 RNA test, before a diagnosis is confirmed (per CDC). Only the ordering clinician can tell you what your specific result means.

What negative, nonreactive, and not detected may mean

These terms generally mean the target was not found, or did not reach the assay's threshold for a positive/reactive call:

• Negative on a NAAT usually means the pathogen's genetic material was not detected in that specimen.
• Nonreactive on antibody-based serology usually means antibodies were not detected at or above the cutoff.
• Not detected is often used on quantitative or molecular reports.

A negative result is meaningful, but it is not universal certainty. Timing matters. Every STI test has a window period — the interval between exposure and when the test can reliably detect infection. Testing too early in this window can produce a nonreactive or "not detected" result even when infection is present (per CDC). For a plain-English overview, see our STI window periods guide and how long after exposure to get tested.

If you have symptoms, a known exposure, or ongoing risk, a negative result does not replace clinician judgment — repeat or additional testing may be recommended (per CDC).

What equivocal, indeterminate, or borderline means

Some reports use these terms when a result falls near the assay's cutoff or cannot be clearly classified as positive or negative:

• Equivocal or borderline often means the numeric signal is near the threshold and cannot be confidently called reactive or nonreactive.
• Indeterminate may appear on confirmatory tests (for example, an indeterminate HIV differentiation assay) when the antibody bands do not meet the criteria for a positive or negative interpretation (per CDC).
• Preliminary may indicate a result that has not yet completed a full testing algorithm.

Equivocal does not automatically mean positive, and it does not automatically mean negative. Depending on the assay and the clinical situation, a clinician may recommend repeat testing on a new sample, a different test method, or waiting a defined interval before retesting (per CDC).

What a reference range means

A reference range is the range of values the laboratory considers expected for a given population and assay. On STI reports, reference ranges show up in several ways:

• Many STI tests are qualitative — the report simply lists Negative / Nonreactive / Not Detected as the reference, and any other result is flagged.
• Some serologic tests display a numeric index with a reference range such as "< 1.00" for nonreactive.
• Quantitative tests (for example, hepatitis viral loads or syphilis titers) show numeric values with test-specific ranges.

Reference ranges are specific to the assay and the laboratory. A value that appears "high" on one report may correspond to a different clinical picture than the same number on a different assay. Always read the range printed on your own report, not a range you found online (per MedlinePlus).

What index values and signal-to-cutoff ratios mean

Some antibody or screening assays print a numeric result — often called an index value, signal-to-cutoff (S/CO) ratio, or optical density ratio. In general, values below a defined cutoff are reported as nonreactive, and values at or above the cutoff are reported as reactive.

The exact cutoff, the interpretation of higher values, and the need for confirmatory testing all vary by assay and by laboratory. There is no universal cutoff that applies across manufacturers or infections, and a single index value is not a diagnosis by itself (per CDC). If your report includes an index value, the ordering clinician can explain how that number fits into the testing algorithm for your specific test.

What titers may mean

A titer is a measurement of how much of a substance — often an antibody — is present in a sample. Titers are typically expressed as dilutions (for example, 1:2, 1:8, 1:32). A higher dilution at which the test is still reactive corresponds to a higher titer.

Non-treponemal titers (such as RPR) are one example: clinicians may follow titer trends over time as part of syphilis staging and treatment-response monitoring (per CDC). A single titer number, on its own, does not tell you whether infection is active, treated, or resolved — the trend and clinical context matter, and interpretation belongs to a qualified clinician.

Why a report may show both screening and confirmatory results

Several STI diagnoses rely on multi-step testing algorithms. The report may show a screening result followed by one or more confirmatory tests:

• HIV: A reactive 4th-generation antigen/antibody screen is followed by an HIV-1/HIV-2 antibody differentiation assay, and sometimes HIV-1 RNA testing, before a diagnosis is established (per CDC).
• Syphilis: Laboratories use either a traditional algorithm (non-treponemal screen followed by treponemal confirmation) or a reverse-sequence algorithm (treponemal screen followed by non-treponemal testing) (per CDC).

If your report has more than one line for the same infection, that is often the algorithm at work — not a contradiction. The ordering clinician interprets the combined result.

Why results may be flagged as abnormal

Laboratory information systems automatically flag results that fall outside the reference range — often with letters such as H (high), L (low), or A (abnormal), or with bold text and asterisks. On an STI report:

• A reactive or detected result is expected to be flagged, because the reference is negative/nonreactive/not detected.
• A flag alone does not mean the result is severe, urgent, or confirmed — it simply means the value is outside the reference category (per MedlinePlus).

Do not read "abnormal" as a diagnosis. Read the actual result value and the reference range, and let the clinician who ordered the test interpret it.

What to do after reading the report

Reading and understanding your report is different from interpreting it. If your result is positive, reactive, detected, equivocal, or otherwise unclear, the next step is a conversation with the ordering clinician or another qualified healthcare professional — see our companion guide, what to do next after a positive or reactive STD test result, for a practical checklist of actions, confirmatory testing considerations, partner-notification basics, and follow-up timing.

If you are choosing where to test in the first place, confidential STD testing explains how private, lab-drawn testing works in the U.S. healthcare system.

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Reminder: LabTestsOnDemand does not diagnose or treat any condition. Our panels are lab-drawn at an in-person Labcorp collection site (not at-home kits). The Standard STI Panel includes 6 tests (HIV, syphilis, hepatitis B, hepatitis C, chlamydia, gonorrhea). The Comprehensive Sexual Health Panel adds HSV-1, HSV-2, and trichomoniasis for 9 tests total. Hepatitis A is not included in either panel.

Frequently asked questions

Does reactive mean positive? Reactive generally means a screening test found what it was looking for, but on many STI assays a reactive result is preliminary and requires confirmatory testing before it is considered a confirmed diagnosis (per CDC). Only the ordering clinician can tell you what your specific reactive result means.

Does nonreactive mean negative? Nonreactive generally means antibodies or antigens were not detected at or above the assay's cutoff. It is often reported as the equivalent of negative for that screening test. However, timing within the window period, symptoms, and recent exposures may still require clinician follow-up (per CDC).

What does "detected" mean on an STI test? On molecular/NAAT reports, detected usually means the pathogen's genetic material was present at or above the limit of detection. The clinical meaning depends on the infection, the specimen site, and the assay used.

What does equivocal mean? Equivocal generally means the numeric signal fell near the assay's cutoff and could not be confidently classified as reactive or nonreactive. Depending on the test, a clinician may recommend repeat testing or a different method (per CDC).

Why is my result marked "abnormal"? Lab systems flag any result outside the reference range as abnormal, high, or low. On STI reports, a reactive or detected result is expected to be flagged — the flag itself is not a severity indicator (per MedlinePlus).

What is an index value? An index value or signal-to-cutoff ratio is a numeric output from some antibody-based assays. Values below the cutoff are typically nonreactive; values at or above the cutoff are typically reactive. Cutoffs and interpretation vary by assay — a single index value is not a diagnosis (per CDC).

What is a reference range? A reference range is the range of values the laboratory considers expected for that specific assay. Many STI tests are qualitative, with a reference of Negative or Nonreactive. Always use the range printed on your own report (per MedlinePlus).

Why are there two results for the same infection? Some infections — HIV and syphilis are common examples — use multi-step algorithms in which a screening result is followed by one or more confirmatory tests. Both lines may appear on the same report (per CDC).

Can a negative result change later? Yes. Testing during a window period may miss an early infection, and new exposures can occur after a test was drawn. If you have symptoms, a known exposure, or ongoing risk, a clinician may recommend repeat testing (per CDC). See our window periods guide for typical timing.

Who should explain my result? The clinician who ordered the test, or another qualified healthcare professional, is the right person to interpret your specific report. Educational articles like this one describe general terminology only.

Sources

• Centers for Disease Control and Prevention — STI Treatment Guidelines, 2021
• Centers for Disease Control and Prevention — Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations
• Centers for Disease Control and Prevention — Syphilis Laboratory Testing
• MedlinePlus (U.S. National Library of Medicine) — Understanding Laboratory Tests
• MedlinePlus — Reference Ranges and What They Mean
• U.S. Preventive Services Task Force — Screening for Chlamydia and Gonorrhea
• Mayo Clinic — Sexually Transmitted Disease (STD) Testing