In shortThe standard is a 4th-generation ELISA: it looks for antibodies and the p24 antigen together. Reliable 6 weeks after a contact, conclusively rules out HIV at 12 weeks. Earlier than 10–14 days only PCR for viral RNA can detect infection. Any positive ELISA is always confirmed by immunoblot.
About the infection
HIV is diagnosed in the laboratory. The screening test is the 4th-generation ELISA, catching both the p24 antigen (a viral protein appearing early) and antibodies (produced later). Rapid tests on a blood drop or saliva are convenient, but any positive result needs laboratory confirmation.
The key concept is the “window”: the time when infection has happened but the test is still negative. Fourth-generation tests have a shorter window than old ones, but not zero — so the timing after contact matters more than the test’s “accuracy”.
Diagnostic methods
| Method | What it shows | When it is used |
|---|---|---|
| 4th-generation ELISA (Ag/Ab) | p24 antigen + antibodies | Standard screening; reliable from 6 weeks, conclusive from 12 |
| Rapid test (blood/saliva) | Antibodies | A 15–20 minute answer; “+” needs laboratory confirmation |
| PCR for HIV RNA | The virus itself in blood | Earliest detection — from 10–14 days; on indications |
| Immunoblot | Confirmation of specific antibodies | Done for any positive screening |
Window period: when the test becomes reliable
The window is the period when infection is present but the test is still negative. RNA PCR — from 10–14 days after contact; 4th-generation ELISA — reliable from 6 weeks; HIV is conclusively excluded by a negative test at 12 weeks (3 months) after the last risky contact.
How to prepare
Venous blood; no special preparation, fasting not required. Testing is anonymous or confidential.
Reading the result
| Result | What it means |
|---|---|
| ELISA negative, > 12 weeks | HIV excluded |
| ELISA negative, < 6 weeks | Too early — retest at weeks 6 and 12 |
| ELISA positive | Not a diagnosis: the result is confirmed by immunoblot in a reference lab |
| Immunoblot positive | HIV confirmed — referral to a specialized center for monitoring and therapy |
When a retest makes sense
After a risky contact: first test at week 6, conclusive at week 12. With ongoing risk, doctors recommend regular testing. After an emergency exposure the doctor may order PCR from day 10–14.
Which specialist to see
A positive or doubtful result is reviewed by: Infectious disease specialist. Note the date of the first test and the possible contact — the retesting plan depends on it.
Several markers on your report?
The app reads your whole report — this marker together with its neighbors, not one by one.
Frequently asked questions
How many days until an HIV test is accurate?
The 4th-generation ELISA is reliable 6 weeks after contact; the conclusive “no HIV” is a negative test at 12 weeks. A test on day 3–5 after contact is not informative.
A positive rapid test — is it definitely HIV?
No. Any positive screening (ELISA or rapid) is confirmed by immunoblot: false-positive reactions occur, especially in pregnancy and autoimmune conditions. No diagnosis is made before the immunoblot.
Does HIV show in a complete blood count?
No. The CBC does not detect HIV: its changes are nonspecific. HIV is detected only by special tests — ELISA, PCR, immunoblot.
Sources
- WHO — Consolidated guidelines on HIV testing services — WHO, 2019 (who.int). Accessed: September 17, 2026.
- MedlinePlus — Hepatitis Panel — MedlinePlus (medlineplus.gov). Accessed: September 17, 2026.