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HIV Antibody and Qualitative P24 Antigen Test (CSF)

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

This test checks for HIV antibodies and the presence of the virus’s protein (p24 antigen) in cerebrospinal fluid (CSF). It helps determine if HIV has affected the central nervous system, such as in meningitis or encephalitis.

Quick summary

["Assesses potential HIV infection in the brain/spinal cord fluids."]

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

Key facts at a glance

LOINC
16977-1
Short code
HIV1 Ag CSF Ql
Synonyms
HIV1 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

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms like severe headaches, confusion, seizures, or neurological issues that could suggest HIV-related brain infections. It’s also used in certain high-risk groups or when monitoring HIV progression in the nervous system.

What to Expect Before the Test

A lumbar puncture (spinal tap) is needed to collect CSF. You’ll lie on your side with your legs bent, and a needle will be inserted into your lower back to draw fluid. You may feel mild pressure or discomfort, but it’s usually brief. Medications can be given beforehand to reduce pain.

What Happens During the Test

The collected CSF is tested for HIV antibodies (using immunoassay) and p24 antigen (via a qualitative method). Results are typically ready within 24–48 hours, depending on lab processing.

What the Results Mean

Positive results for HIV antibodies or p24 antigen indicate active HIV infection in the CNS. Negative results mean no detectable HIV in this sample, but further testing may still be needed for broader diagnosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

HIV CSF Screen

Frequently asked questions

Will this test show HIV in my blood?
No. This test specifically looks for HIV in cerebrospinal fluid, not blood. Blood tests (like HIV antibody tests) are used for general infection screening.
What if my results are positive?
A positive result means HIV is likely present in your CNS. Your doctor will likely order additional tests (e.g., blood tests, imaging) to confirm and guide treatment. Follow-up care with an infectious disease specialist is recommended.
Can I still get HIV if I have this test?
Yes. This test only checks for existing HIV in your CSF. You can still be infected through exposure (e.g., unprotected sex, sharing needles) and develop symptoms later. Practice safe behaviors to prevent transmission.
  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