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HIV p24 Antigen, Serum/Plasma

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

This test detects the p24 protein, a fragment of the HIV virus, in your blood or body fluids. It helps screen for HIV infection early.

Quick summary

["Early HIV detection with a simple blood test to support timely care."]

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

Key facts at a glance

LOINC
18396-2
Short code
HIV1 p24 Ag SerPl Ql IA
Synonyms
HIV1 p24 Ag SerPl Ql IA
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
CPT
86701
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What Is the Purpose of This Test?

This test is used primarily to screen for HIV infection by identifying the presence of the p24 protein, which is a part of the virus. It can help detect HIV earlier than some other tests, even before antibodies develop, though it is not as sensitive alone as antibody tests.

How Is the Sample Collected?

A blood sample is drawn from a vein, usually in your arm, using a small needle. You may feel a brief pinch, but the procedure is quick and typically done in a clinic or lab setting.

What Does a Positive Result Mean?

A positive result indicates the presence of the HIV p24 antigen, suggesting active HIV infection. However, false positives are rare, so follow-up testing is usually recommended to confirm the diagnosis.

What If My Result Is Negative?

A negative result means the p24 antigen was not detected in your sample at this time. However, HIV can still be present if antibodies have not yet developed, so retesting after a few weeks is advised if you suspect exposure.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

HIV p24 Ag

Frequently asked questions

Why Might I Need This Test?
Your healthcare provider may recommend this test if you have symptoms suggestive of HIV (e.g., fever, fatigue), have had unprotected sex or shared needles, or are at higher risk for HIV due to lifestyle or medical history. Early detection is critical for managing the virus effectively and preventing complications.
How Soon After Exposure Should I Get Tested?
If you suspect recent exposure to HIV, testing within 4–6 weeks after exposure is recommended. However, the p24 antigen test may not detect HIV immediately after exposure, so antibody tests are often used for earlier confirmation.
Can This Test Be Used to Monitor HIV Treatment?
No, this test is primarily for screening and diagnosing HIV infection, not for monitoring treatment response. Other tests, such as viral load or antibody tests, are used to track HIV progression and treatment effectiveness.
  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