HIV screening by ELISA: What does the standard diagnostic ELISA primarily detect in patient specimens?

Introduction / Context:
First-line laboratory screening for HIV infection traditionally uses ELISA to detect host antibodies against viral antigens. Understanding what the assay measures is key for interpreting window periods and confirmatory testing algorithms.

Given Data / Assumptions:

• “Standard” ELISA refers to classic antibody detection, not fourth-generation antigen/antibody combo tests.
• Patient sample is serum or plasma.
• Confirmatory tests (e.g., Western blot historically, now immunoassays/NAAT) follow positives.

Concept / Approach:
Traditional ELISA screens for anti-HIV antibodies. Seroconversion timing creates a diagnostic window before antibodies appear; thus a negative early test does not exclude acute infection, highlighting why antigen (p24) or RNA tests are used in later generation algorithms.

Step-by-Step Solution:
Solid-phase HIV antigens capture patient anti-HIV antibodies if present.Enzyme-labeled anti-human Ig detects bound antibodies.Color development indicates presence of anti-HIV antibodies.Therefore, the assay measures antibody to HIV.

Verification / Alternative check:
Fourth-generation assays additionally detect p24 antigen, but the question specifies the ELISA’s intended measurement in its classic form.

Why Other Options Are Wrong:

• HIV antigen or free virus requires antigen capture or nucleic acid tests.
• HLA antibodies are unrelated to HIV screening.

Common Pitfalls:
Assuming all ELISAs are identical; generations differ in targets (antibody only vs antigen/antibody combo).

Final Answer:
Antibody to HIV only