What is the viral marker used to measure early HIV replication?

AIIMS CRE 2025

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS CRE 2025

Explanation

The p24 antigen is a structural core protein (capsid protein) of the HIV virus.
It becomes detectable in the blood approximately 2-3 weeks after infection, which is earlier than the appearance of HIV antibodies.
This early appearance makes it a crucial marker for diagnosing acute HIV infection during the 'window period'.
Fourth-generation HIV screening tests combine the detection of p24 antigen with HIV antibodies to improve early diagnosis.

Option A: Hemoglobin is a protein in red blood cells that transports oxygen. It is not a component of the HIV virus and does not measure viral replication.
Option C: Platelets are cell fragments involved in blood clotting. While HIV can cause thrombocytopenia (low platelet count), it is a non-specific hematological finding, not a direct measure of viral replication.
Option D: CD8 cells are a type of T-lymphocyte, which are part of the host's immune system that attacks virus-infected cells. They represent the body's response to the virus, not a part of the virus itself.

Visual 1: Timeline Graph - A graph showing the typical course of HIV infection, plotting the levels of HIV RNA (viral load), p24 antigen, and HIV antibodies over time from the point of infection. This would visually demonstrate that p24 antigen peaks and becomes detectable before antibodies.
Visual 2: Diagram - A simplified diagram of the HIV virion structure, clearly labeling the p24 capsid protein in the core. This helps learners understand that p24 is a physical component of the virus.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Early Diagnostic Markers for HIV as background academic context rather than a clinical decision trigger.
Early diagnosis of HIV using markers like p24 antigen is critical for public health. It allows for prompt initiation of antiretroviral therapy (ART), which improves patient outcomes and reduces the risk of transmission to others.
Nurses play a key role in educating patients about HIV testing, explaining the meaning of different test results (including the window period), and providing counseling and support.
What if the question asked for the earliest possible marker of HIV infection? The answer would be HIV RNA (viral load), which can be detected by Nucleic Acid Tests (NAT) as early as 10-12 days post-infection, even before the p24 antigen becomes prominent.

How to Approach the Question

First, analyze the question's keywords: 'viral marker' and 'early HIV replication'.
'Viral marker' implies a substance that is part of the virus itself or is produced in direct response to its replication.
'Early' points to the initial phase of infection, before a full-blown immune response (like antibody production) is established.
Evaluate each option: Hemoglobin and Platelets are general blood components, not specific to any virus. Eliminate them.
Compare p24 antigen and CD8 count. CD8 is a host immune cell, not a 'viral' marker. p24 antigen is a protein component of the HIV virus itself.
Conclude that p24 antigen is the only option that is both a component of the virus and a known marker for early infection.

Concept Tested & Keywords

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