Quick overview
HIV can be tested reliably — at home with self-tests, on site with rapid tests, and in the laboratory. Timing matters because each method has a window period during which a recent infection may not yet be detected. Knowing the strengths and limits of each method helps you interpret results realistically and avoid missteps. Good starting points: CDC, NHS, WHO, and UK guidance from Terrence Higgins Trust.
Test types at a glance
HIV self-test (at home)
Antibody rapid test with a result in around 15 minutes; legally available in the UK from pharmacies and reputable online retailers. Any reactive (positive) result must be confirmed by a laboratory test. See THT on HIV self-testing.
Professional rapid test
Antibody or antigen/antibody combination test performed by trained staff; results in minutes. Reactive results are routinely confirmed by a laboratory test. Overview: NHS.
Fourth-generation laboratory test
Combines p24 antigen and antibodies. Detects infection earlier than antibody-only tests and is the clinical standard for early diagnosis. More at UKHSA guidance and NHS.
Nucleic acid test (HIV-1 RNA/NAT)
Direct detection of the virus; the earliest method to turn positive, used particularly after very recent exposure or when results are unclear. See UKHSA.
Window periods & detection limits
| Test type | Typical time to detection (window) | References |
|---|---|---|
| Self-test (antibodies) | about 23–90 days after exposure | CDC, FDA (OraQuick) |
| Lab test, 4th gen. (Ag/Ab) | about 18–45 days | CDC, NHS |
| RNA/NAT | about 10–33 days | CDC |
These ranges are indicative. A negative result before the relevant window has closed does not exclude infection. A short explainer: CDC patient leaflet on window periods (PDF).
Accuracy in practice
Quality-assured self- and rapid tests have very high specificity; false positives are uncommon and are resolved by confirmatory laboratory testing. Sensitivity depends strongly on timing: the closer to the event, the higher the risk of a false negative. Fourth-generation laboratory tests are more sensitive in early phases than antibody-only tests. See NHS and the WHO 2024 update.
Oral self-tests vs blood tests
Oral-fluid tests are accessible and convenient. In very early infection, blood-based methods (finger-prick, laboratory) tend to be informative sooner. If you want the earliest clarity, favour blood tests — or go straight to a 4th-generation laboratory test. UK orientation: NHS, Terrence Higgins Trust.
Interpreting results correctly
Negative
Reliable once the window for the chosen test has clearly passed and there has been no new exposure in between. Otherwise, retest later or seek earlier clarification with a 4th-generation laboratory test or RNA/NAT.
Reactive or positive
A reactive result from a self- or rapid test is confirmed in the laboratory. Only the confirmatory result is diagnostic.
Invalid
Repeat with a new kit and follow instructions, storage and read-time exactly. If unsure, get a professional test.
Sex after a negative test: what is safe and what is not?
A single negative self- or rapid test soon after possible exposure is not a guarantee of safety. During the window period the test may lack detectable targets, while viral load — especially early on — can be high. A negative early result therefore does not exclude transmission.
Practical quick guide
- Before the window closes: use protection. For earlier clarification, choose a 4th-gen laboratory test; in the very earliest phase, consider RNA/NAT.
- After the window: a negative is reliable provided no new exposure occurred.
- Treatment and U=U: with sustained undetectable viral load on effective treatment, HIV is not transmitted during sex. This relies on regular laboratory values, not home-test results.
- PrEP/PEP: may change test type and timing; confirm with a clinician.
Negative yet infectious?
In the early phase after possible exposure, an antibody self-test can still be negative despite infection, because the body has not produced enough antibodies. That says nothing about actual viral load; early on it can be high, increasing transmissibility. An early negative is not a green light for unprotected sex. If you need rapid certainty, choose a 4th-generation laboratory test or RNA/NAT and stay cautious until the diagnosis is clear. For partners where HIV is known and treated, the rule is: if viral load is durably undetectable, HIV is not transmitted during sex — provided this is backed by stable, documented laboratory results.
Information for the UK
HIV self-tests are lawful to sell and use in the UK. The ban on sale of HIV self-testing kits was lifted in 2014, and CE-marked self-tests (regulated by the MHRA) have been commercially available since 2015. Guidance on test types, window periods and diagnostic pathways is provided by the NHS and by UK Health Security Agency (UKHSA). Free or low-barrier testing — including postal kits and community testing — is offered through NHS services and partners such as Terrence Higgins Trust.
Practical testing strategy
- First check: a self-test with careful adherence to the instructions. Always interpret the result against the relevant window period.
- Early clarification: when little time has passed since exposure, prefer a 4th-generation laboratory test; in the very earliest phase, RNA/NAT can be considered.
- Ongoing need: a simple, predictable rhythm (for example every 3–6 months for a laboratory screen) works well for many people.
- Golden rule: confirm any reactive self- or rapid test in the laboratory; if uncertain, seek clinical advice.
Common mistakes & limits
- Testing too early within the window can create a false sense of security.
- Home-test errors (sampling, read-time, storage) can distort results.
- Product choice: look for CE marking, trustworthy vendors and clear instructions.
- Oral vs blood: oral tests are more convenient; blood-based methods are often informative earlier.
Extras: PrEP/PEP & testing
With ongoing or recently started PrEP, and after PEP, the timing and choice of tests can differ. See interval and algorithm guidance from the UKHSA and WHO, and confirm the plan with your clinician.
Conclusion
HIV self-tests are quick, discreet and useful for an initial read. For the earliest robust answer, fourth-generation laboratory tests have an edge; after very recent exposure, RNA/NAT provides the earliest detection. If you respect window periods, confirm reactive results, and choose quality-assured products, you will test safely and reliably. Good starting points: NHS, UKHSA, WHO, Terrence Higgins Trust.