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Cryptococcal Antigen (Serum/Plasma) - Qualitative

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

This test detects the presence of cryptococcal antigen, a fungal marker often found in the blood or body fluids of people with cryptococcal meningitis or other cryptococcal infections.

Quick summary

["A positive result may indicate a fungal infection requiring medical evaluation."]

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

Key facts at a glance

LOINC
100123-9
Short code
C pneum IgA Ser Ql IA
Synonyms
C pneum IgA Ser 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
82784
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

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms of a fungal infection, such as fever, headache, confusion, or neurological symptoms. It’s also used in people with weakened immune systems, like those with HIV/AIDS, to monitor for cryptococcal meningitis or other infections caused by *Cryptococcus* yeast.

What to Expect Before the Test

No special preparation is needed. The blood sample is typically drawn from a vein in your arm. If you’re taking blood tests frequently, let your healthcare provider know to avoid drawing blood from the same arm.

What the Test Results Mean

A positive result means cryptococcal antigen was detected in your sample. This can help confirm a fungal infection and guide treatment decisions. A negative result means no antigen was found, but further testing or monitoring may still be needed depending on your symptoms and medical history.

Common Causes of Positive Results

Positive results are most commonly linked to cryptococcal meningitis or other cryptococcal infections. Rarely, false positives can occur, especially in people with certain medical conditions or those taking specific medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Crypto Ag (Serum/Plasma) - Qualitative

Frequently asked questions

What does a positive result mean for my health?
A positive result suggests you may have an active cryptococcal infection, which requires prompt medical attention. Your doctor will likely recommend further testing, such as a lumbar puncture to examine cerebrospinal fluid, and may start antifungal treatment immediately.
Can this test be used to monitor treatment?
Yes, this test can help monitor the effectiveness of antifungal treatment. Repeated testing may be needed to check if the infection is improving or if treatment needs adjustment.
Is this test covered by insurance?
Insurance coverage depends on your specific plan and medical reason for testing. Check with your insurance provider or healthcare provider to confirm coverage details before the test.
  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