Cryptococcal antigen test
Quick answer: This test looks for a protein (antigen) of Cryptococcus, a fungus that can cause meningitis, in blood or spinal fluid. Doctors order it when cryptococcal meningitis is suspected, especially in people with HIV or weak immunity.
- SampleBlood or CSF (spinal fluid)
- TakesAbout 5 minutes for blood; 20 to 30 minutes for a lumbar puncture
- Before the testNo special preparation is usually needed for the blood test; a CSF sample is collected by a doctor through a lumbar puncture.
How the test is done
- 1For blood, a nurse draws a tube from your arm
- 2For spinal fluid, a doctor does a lumbar puncture
- 3The sample is tested for the Cryptococcus antigen
- 4A positive result may be diluted to give a titre
What your results can mean
Reading your report
The report usually says positive, negative or borderline; a positive result often needs a confirmatory test, so discuss it with your doctor.
If the result is outside the usual range
A positive result can point to cryptococcal infection, including meningitis, which needs urgent treatment. In people with advanced HIV, a positive blood result can show infection before symptoms appear.
Who usually has this test
People with HIV and a low CD4 count, and people with weak immunity who have headache, fever or confusion.
Risks and aftercare
Nothing special after blood; after a lumbar puncture, rest and drink fluids as advised.
Names and options
Also called: CrAg, cryptococcus antigen, crypto antigen
Options
- Serum
- CSF
Listed by the hospital as
- CRYPTOCOCCUS ANTIGEN (QUALITATIVE), CSF
- CRYPTOCOCCUS ANTIGEN, (QUALITATIVE), SERUM
Questions about this test
Why are some people with HIV screened for cryptococcal antigen?
In advanced HIV, cryptococcal infection can be found in the blood weeks before meningitis. Early treatment can prevent serious illness.
What is cryptococcal meningitis?
It is a fungal infection of the lining of the brain. It can cause headache, fever, neck stiffness and confusion, and needs hospital treatment.
How do people catch Cryptococcus?
The fungus lives in soil and bird droppings and is breathed in. It mainly causes illness in people with weak immunity.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.