What this test measures
The Cryptococcus Latex Agglutination test detects the polysaccharide capsular antigen of Cryptococcus neoformans (and C. gattii) — the major fungal pathogen causing meningitis in immunocompromised patients, particularly those with advanced HIV (CD4 count <100). Latex particles coated with anti-cryptococcal antibody agglutinate visibly in the presence of the antigen, giving a result within minutes. Modern lateral flow assay (LFA) versions give the same result in a 10-minute strip format.
The test can be performed on serum (blood), CSF (cerebrospinal fluid), or urine. CSF is the most sensitive sample in suspected meningitis. The result is reported as positive / negative with a titre (e.g. 1:64), which correlates with fungal burden — high titres indicate disseminated disease and worse prognosis.
Why it matters
Cryptococcal meningitis is one of the leading causes of death in late-stage HIV/AIDS, particularly in sub-Saharan Africa and India. WHO recommends serum CrAg screening for all adults with HIV and CD4 count <200 — a positive result identifies pre-symptomatic disease and allows pre-emptive fluconazole treatment to prevent progression to meningitis. The test is also used in: (1) any HIV-positive patient with headache, fever, or altered mental state; (2) immunocompromised patients (transplant recipients, chronic steroid users, haematological malignancy); (3) anyone with subacute or chronic meningitis of unclear cause.
In India, India's National AIDS Control Programme has integrated CrAg screening into HIV care for advanced disease. The latex test is widely available in NABL-accredited labs, and the LFA version is increasingly common at point-of-care.
How to prepare
No fasting required. CSF sample requires a lumbar puncture, done in a hospital setting; serum can be collected by routine venepuncture. Disclose HIV status, CD4 count, any current antifungal treatment, and recent fluconazole exposure.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Cryptococcal Antigen[1][2] | Negative | Negative — Cryptococcus disease very unlikely if test is sensitive (LFA on serum has sensitivity ~99% in HIV with meningitis). Repeat or culture if clinical suspicion remains. | Positive — Cryptococcal infection. Titre correlates with disease burden: low titre (1:8 to 1:64) — early or treated disease; high titre (>1:512) — heavy fungal burden, disseminated disease, worse prognosis. CSF positive = cryptococcal meningitis (treat with amphotericin + flucytosine or fluconazole induction). Serum positive in asymptomatic HIV+ patient = pre-emptive fluconazole treatment. |
Cryptococcal antigen testing — sample and clinical implications
| Sample | Use | Action if positive |
|---|---|---|
| Serum (HIV CD4 < 200, asymptomatic) | Pre-emptive screening | Lumbar puncture; start fluconazole if no meningitis |
| Serum (symptomatic patient) | Suspected cryptococcal disease | LP for CSF testing + induction antifungal therapy |
| CSF (suspected meningitis) | Most sensitive for meningitis | Confirms diagnosis; amphotericin + flucytosine induction |
| Urine | Less commonly used | Confirms positive if serum / CSF positive |
| Titre > 1:512 in serum | Indicates high burden / disseminated disease | Aggressive induction therapy + management of raised ICP |
Frequently asked questions
Who needs cryptococcal antigen testing?
Any HIV-positive patient with CD4 count <200 (especially <100) — for screening; anyone with HIV plus headache, fever, neck stiffness, or altered consciousness; any immunocompromised patient with suspected meningitis.
Is it the same as a culture?
No — antigen testing detects the polysaccharide capsule. Fungal culture grows the organism (takes 3–7 days). CrAg is faster (minutes) and very sensitive in HIV-associated cryptococcosis. Culture remains the gold standard for confirmation.
Do I need to fast?
No.
My serum CrAg is positive but I have no symptoms — what now?
A positive serum CrAg in an asymptomatic HIV patient is a major finding. The next step is a lumbar puncture to check for meningitis; if negative for meningitis, fluconazole pre-emptive therapy is started for several months along with ART.
How sensitive is the latex test?
In CSF for cryptococcal meningitis, sensitivity exceeds 95%. In serum (especially LFA format), sensitivity is also >95% in HIV-positive patients. Negative tests are highly reliable in this setting.
Can the test give false positives?
Rare. Rheumatoid factor can cause false positives in older latex assays; modern LFA versions have minimal cross-reactivity. The titre helps — very low titres (1:2 to 1:4) may need confirmation.
What is the treatment if positive?
Antifungal therapy. Standard induction: amphotericin B + flucytosine for 2 weeks, then high-dose fluconazole consolidation for 8 weeks, then maintenance fluconazole. For asymptomatic serum-positive patients, fluconazole alone may be sufficient.
How fast is the report?
Latex agglutination: 30 minutes. LFA strip: 10 minutes. Most NABL labs report formally within 2–4 hours.
Related Coagulation tests
Tests commonly ordered alongside CRYPTOCOCCUS LATEX AGGLUTINATION, or that help interpret an unexpected result.
Sources & references
- CDC — Cryptococcal Disease · accessed 2026-05-30T00:00:00.000Z
- IDSA Guidelines — Cryptococcal Disease · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Cryptococcosis · accessed 2026-05-30T00:00:00.000Z
- WHO — Cryptococcal Disease in HIV · accessed 2026-05-30T00:00:00.000Z
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