Not reliably on its own. A Western blot detects antibodies to HIV and was historically used to confirm positive screening tests, but it can give indeterminate or false-positive results and is no longer the preferred standalone confirmatory method in many guidelines. Modern confirmation uses antigen/antibody differentiation assays and nucleic acid (RNA) tests; diagnosis should follow recommended confirmatory testing and clinical assessment.

ELISA is a fast, highly sensitive screening test that detects HIV antibodies (or p24 antigen) by enzyme-linked reactions in a plate; it can yield false positives. Western blot is a slower, more specific confirmatory test that separates viral proteins by electrophoresis and detects antibodies to individual HIV protein bands, reducing false positives. Western blot is now less commonly used, replaced by combination antigen/antibody and nucleic acid tests.

Western blot results typically take a few days to a week. Many laboratories report results within 1–3 days, but if samples are sent to a reference lab or confirmatory steps are needed it can take up to 7–10 days. An indeterminate result requires extra testing (repeat antibody tests or PCR), which lengthens the wait. Ask your clinic or lab for their usual turnaround and next steps.

A fourth‑generation laboratory HIV antigen/antibody (Ag/Ab) test is the preferred initial test because it detects p24 antigen and antibodies early. Reactive results should be confirmed with an HIV‑1/HIV‑2 antibody differentiation assay; if that is indeterminate or discordant, a nucleic acid (HIV RNA) test is used to resolve diagnosis. Testing should be done through accredited labs and followed by clinical consultation.

Western blot has been largely replaced because modern fourth‑generation antigen/antibody immunoassays and HIV‑1/2 differentiation tests, plus nucleic acid testing, are faster, more sensitive (especially in early infection), more specific, automated and easier to interpret. Western blot gave indeterminate or false‑negative results in acute infection, was time‑consuming, costly and less reproducible, so algorithms now use newer validated tests.

The cost of an HIV Western blot varies widely by country and provider. Public programs (for example national health services) often provide it free or subsidized. In private labs costs range approximately: India ₹500–₹2,000, the US $100–$300, and private UK clinics £40–£150. Availability is declining because newer confirmatory assays are commonly used, so prices and access vary.