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HIV p24 Antigen (Qualitative) - Serum/Plasma

Published: August 9, 2026Updated: August 16, 2026

This test detects the presence of HIV p24 antigen in your blood, which is a protein produced by the virus shortly after infection. It helps determine if you have an active HIV infection.

Quick summary

["This test can help identify early HIV infection before antibodies develop."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
49718-0
Short code
HIV1 p24 Ag CSF Ql
Synonyms
HIV1 p24 Ag CSF Ql
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
86701
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

What Is HIV p24 Antigen Testing Used For?

HIV p24 antigen testing is primarily used as part of an initial screening for HIV infection. It can detect the virus within days to weeks after exposure, sometimes before antibodies appear. This test is often used in combination with other tests for more accurate diagnosis.

How Does This Test Work?

The test uses an immunoassay (a type of antibody test) to identify the HIV p24 antigen in your blood. When HIV infects a person, it produces the p24 protein, which is captured by the test to confirm infection.

What Does a Positive Result Mean?

A positive result means the test detected HIV p24 antigen, indicating an active HIV infection. Further testing with antibody tests may be needed to confirm the diagnosis and determine the stage of infection.

What Does a Negative Result Mean?

A negative result means the test did not detect HIV p24 antigen at the time of testing. However, HIV infection can take time to develop detectable antigen levels, so retesting may be recommended if there is a risk of exposure.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

HIV p24 Ag

Frequently asked questions

When Might I Need This Test?
You may need this test if you have recently been exposed to HIV, have symptoms of infection (like fever, fatigue, or swollen lymph nodes), or if your healthcare provider suspects HIV based on other risk factors.
What Are Common Symptoms of HIV Infection?
Symptoms of early HIV infection can include flu-like symptoms such as fever, chills, fatigue, swollen lymph nodes, muscle aches, and sore throat. However, many people may not experience symptoms at all.
How Soon After Exposure Can This Test Detect HIV?
This test can detect HIV p24 antigen within 2 to 8 weeks after exposure, depending on the individual. Antibody tests may take longer to become positive, sometimes up to 3 to 6 months.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy