References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Modern STI tests are highly accurate when used correctly and at the right time after exposure. Most rely on nucleic acid amplification (NAAT) or advanced antibody/antigen detection, giving sensitivity and specificity of over 95% for the main infections. Knowing the accuracy of different tests — and the factors that can affect them — helps you trust your results.
Here’s a practical guide.
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Accuracy by Test Type
| Test | Sensitivity (catches true positives) | Specificity (avoids false positives) |
|---|---|---|
| 4th-gen HIV lab test | Over 99% | Over 99% |
| Rapid HIV self-test | Around 99% | Around 99.8% |
| Chlamydia NAAT | 95-98% | Over 99% |
| Gonorrhoea NAAT | 95-98% | Over 99% |
| Syphilis blood test | Over 95% | Over 98% |
| Herpes swab (active lesion) | High when fresh | High |
| Herpes blood antibody | Variable | Lower specificity |
What Sensitivity and Specificity Mean
- Sensitivity — how often the test correctly identifies people who are infected
- Specificity — how often the test correctly identifies people who aren’t infected
Both matter. A highly sensitive test catches almost all real infections. A highly specific test avoids false alarms.
What Can Affect Accuracy?
Timing
Testing during the window period (before the infection is detectable) is the biggest cause of false negatives. Always test at the appropriate time for each infection.
Sample quality
Poor sample collection — not enough urine, incorrect swab technique, testing when you’ve recently urinated — can reduce accuracy.
Test type
Lab NAAT is more sensitive than rapid lateral flow tests. 4th-generation HIV tests are more sensitive than older 3rd-generation tests.
Cross-reactivity
Some conditions (recent vaccination, autoimmune disease, pregnancy) can cause rare false positives that are ruled out by confirmatory testing.
False Positives
False positives happen but are uncommon with modern tests. Any positive result should be confirmed with a second test before treatment decisions are made. Clinics routinely do this for HIV and other serious diagnoses.
False Negatives
More common than false positives, usually because of testing too early after exposure. Retesting at the right time gives a more reliable answer.
Tips for Accurate Results
- Test at the right time — wait out the window period
- Use a lab-based test for the most sensitive results
- Follow sample collection instructions carefully
- Include all relevant sites (throat, rectal) if you’ve had those types of sex
- Confirm positive results before acting on them
- Retest if symptoms develop despite a negative result
Are Home Tests as Accurate?
Lab-processed home kits use the same techniques as clinics and are highly accurate. Rapid home self-tests (like lateral flow) are slightly less sensitive but still reliable when past the window period.
Read more: Rapid HIV test accuracy | HIV window period | Home HIV testing
Frequently Asked Questions
Can STI tests be wrong?
Rarely, when used correctly. The most common cause of misleading results is testing too early.
Which STI tests are most accurate?
Lab-based NAAT and 4th-generation HIV tests are considered the gold standard.
Should I get a test of cure?
For most STIs, no. Test of cure is recommended for pharyngeal gonorrhoea, mycoplasma genitalium and chlamydia in pregnancy.
Related reading
- How Accurate Are Rapid HIV Tests?
- Anonymous STI Testing: What It Means
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- Are STI Blood Tests Accurate?
- Before You Get Intimate: Why You Should Ask About STI Testing
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
