Cryptococcus Antigen

Bacterial/ Viral

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No Fasting Required

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Detects cryptococcal infection.

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Cryptococcus Antigen Test - Comprehensive Medical Guide

Why is it done?
- Detects cryptococcal polysaccharide antigen in blood, cerebrospinal fluid (CSF), or urine to identify Cryptococcus neoformans infection
- Diagnose cryptococcal meningitis, particularly in immunocompromised patients such as those with HIV/AIDS, organ transplant recipients, or patients on immunosuppressive therapy
- Screen for cryptococcal fungemia in patients with CD4+ counts below 100 cells/μL who are not receiving antifungal prophylaxis
- Monitor treatment response and prognosis in patients with confirmed cryptococcal infection
- Evaluate patients presenting with fever, headache, neck stiffness, and altered mental status suggestive of meningitis
- Typically performed urgently when cryptococcal infection is suspected, or as part of routine screening in high-risk populations
Normal Range
- Normal Result: Negative or <1:8 titre (no detectable cryptococcal antigen)
- Units of Measurement: Titre or dilution (expressed as 1:8, 1:16, 1:32, 1:64, 1:128, 1:256, etc.) or reported as positive/negative
- Positive Result: ≥1:8 titre or detection of cryptococcal antigen indicates active or recent cryptococcal infection
- Interpretation Guide: Negative results essentially rule out cryptococcal infection; positive results confirm cryptococcal antigenemia or meningitis; higher titres correlate with greater antigenic load and typically indicate more severe disease
- Test Sensitivity: 95-100% for CSF in cryptococcal meningitis; 90-95% for serum antigen; lower sensitivity in urine specimens
Interpretation
- Negative Antigen Test: Effectively rules out active cryptococcal infection; low likelihood of cryptococcal meningitis or fungemia; however, early infection may produce false negatives before antigen production reaches detectable levels
- Low Titre Positive (1:8 to 1:32): Indicates cryptococcal antigenemia; suggests pulmonary infection with hematogenous dissemination or early meningitis; requires clinical correlation and CSF evaluation; associated with lower fungal burden
- Moderate to High Titre Positive (≥1:64): Indicates significant fungal load; strongly suggestive of cryptococcal meningitis or disseminated disease; associated with worse prognosis; requires immediate initiation of antifungal therapy
- CSF-Positive with Serum-Negative: Indicates localized CNS infection; cryptococcal meningitis confirmed; CSF is most sensitive and specific specimen for CNS disease
- Factors Affecting Results: Immunosuppression level (lower CD4 counts associated with higher antigen levels); timing relative to symptom onset; antifungal therapy initiation may cause paradoxical antigen rise before decline; specimen type (CSF most sensitive, followed by serum, then urine); specimen collection and handling procedures
- Clinical Significance: Positive antigen has high specificity (>99%) for active cryptococcal infection; titre correlates with prognosis and fungal burden; baseline titre and subsequent titre trends predict treatment response; persistently positive or rising titres may indicate treatment failure or immune reconstitution inflammatory syndrome (IRIS)
Associated Organs
- Primary Organ Systems: Central nervous system (CNS/brain and meninges), lungs (respiratory tract), blood/vascular system; disseminated disease can involve kidneys, bone marrow, prostate, and lymph nodes
- Medical Conditions Associated with Abnormal Results: Cryptococcal meningitis (subacute or chronic meningitis); cryptococcal pneumonia (pulmonary infection with antigen detectability in serum); disseminated cryptococcosis; cryptococcal antigenemia in asymptomatic patients with profound immunosuppression
- Diseases Diagnosed or Monitored: AIDS-associated cryptococcal disease (most common opportunistic fungal infection in advanced HIV); cryptococcal disease in organ transplant recipients; cryptococcal infection in patients on prolonged corticosteroid therapy; disseminated cryptococcal infection in immunocompromised hosts
- Potential Complications of Abnormal Results: Untreated cryptococcal meningitis leads to fatal infection; increased intracranial pressure and hydrocephalus in CNS disease; death if therapy delayed; immune reconstitution inflammatory syndrome (IRIS) upon immune recovery; chronic sequelae including cognitive impairment, hearing loss, and visual disturbances from CNS involvement; relapse in patients with inadequate therapy or immune suppression
- Risk Factors for Positive Results: HIV infection with CD4+ count <100 cells/μL; organ transplantation; prolonged corticosteroid use; hematologic malignancies and chemotherapy; severe malnutrition; environmental exposure to Cryptococcus neoformans (bird droppings, soil)
Follow-up Tests
- If Antigen Positive - Immediate Follow-up: Lumbar puncture with CSF analysis (glucose, protein, cell count); CSF cryptococcal antigen testing (more sensitive than serum for meningitis); CSF culture for Cryptococcus neoformans; fungal blood cultures; India ink staining of CSF (may show cryptococcal organisms); CD4+ count if HIV status unknown
- Diagnostic Imaging: Brain MRI to evaluate for cryptococcal meningitis, hydrocephalus, or parenchymal involvement; chest X-ray or CT to assess for pulmonary cryptococcosis if not already evaluated
- Baseline Monitoring During Treatment: Repeat serum cryptococcal antigen testing at 2 weeks, 4 weeks, and 10 weeks after therapy initiation to assess treatment response; CSF antigen testing at similar intervals for meningitis; declining titre indicates response to therapy
- Complementary Laboratory Tests: Cryptococcal culture (gold standard but slower); HIV antibody testing or HIV RNA viral load; fungal susceptibility testing for antifungal resistance; inflammatory markers (CRP, procalcitonin); liver and kidney function tests (baseline for treatment planning); CD4+ and CD8+ counts
- Monitoring After Treatment Completion: Periodic antigen testing (every 3-6 months) during maintenance therapy to detect relapse or treatment failure; repeat lumbar puncture at end of induction therapy for meningitis; ongoing CD4+ monitoring in HIV patients to assess immune recovery; assessment for IRIS symptoms
- If Antigen Negative: Alternative diagnosis investigation; consider culture if high clinical suspicion persists; evaluate for other causes of meningitis or fever; may repeat serum and CSF antigen if early infection suspected
Fasting Required?
- Fasting Status: No fasting required
- Specimen Collection: Blood sample: standard venipuncture with serum separator tube (gold-top) or EDTA tube; collected at any time of day; no preparation needed
- CSF Collection (if applicable): Lumbar puncture procedure performed by physician; fluid collected in sterile tube; no fasting required but patient should have informed consent and understanding of procedure
- Urine Collection (if applicable): Clean-catch midstream urine or 24-hour urine collection as directed; no fasting required
- Medication Considerations: No medications need to be held or avoided before specimen collection; continue all routine medications unless directed otherwise by healthcare provider; antifungal therapy should not be delayed for test collection
- Special Preparation Instructions: Remain calm and seated for 15 minutes after venipuncture to prevent syncope; follow facility-specific post-lumbar puncture precautions if CSF collection performed (bed rest, hydration); handle specimens with universal precautions; expedite specimen transport to laboratory; communicate urgency of testing to laboratory if acute infection suspected

How our test process works!