Overview
Cryptococcus (neoformans/gattii complex and related) is an encapsulated yeast detected in the laboratory by capsule microscopy, cryptococcal antigen assays, and culture/identification, interpreted with specimen site and method limits, without antifungal selection.
Classification
| Evidence layer | Typical use | Claim limit |
|---|---|---|
| Capsule prep (ink) | Rapid CSF visual clue | Insensitive; not final ID |
| CrAg | CSF/serum adjunct | Follow IFU cutoffs/prozone notes (local) |
| Culture/ID | Confirmation + isolate | Slow; report status clearly |
| Respiratory isolate | Possible disease or colonization | Needs host/clinical correlation |
Morphologic Features
Round yeast with polysaccharide capsule appearing as a clear halo on negative stains. Narrow-based budding may be seen. Distinguish from artifacts and from Candida (typically no large capsule; different antigen pathway).
Laboratory Characteristics
- Mucoid colonies on fungal media
- Urease-positive clue (confirm ID locally)
- Bird-seed agar brown colonies, availability varies
- MALDI/biochemical/molecular ID per SOP
Reference Intervals
CrAg qualitative cutoffs, titer reporting practices, serum-versus-CSF testing algorithms, and critical-notification lists are assay- and institution-specific, verify current SOP and package inserts.
Clinical and Laboratory Significance
Concordant CSF antigen and culture strongly support cryptococcal meningitis frameworks. Smear-only or antigen-only stages need carefully worded preliminary reports per institutional policy.
Differential Considerations
Differentiate Cryptococcus from Candida and other yeasts, from capsule-like artifacts on ink, and from bacterial meningitis patterns on Gram stain. Pulmonary isolates require disease-versus-colonization framing.
Comparison Tables
Cryptococcus evidence stages
| Finding | Laboratory meaning | Do not claim |
|---|---|---|
| Ink equivocal, CrAg pending | Incomplete stack | Cryptococcus excluded |
| CSF CrAg reactive | Strong adjunct evidence (assay limits) | Drug regimen / dose |
| Culture pending | Confirmation pathway open | Final species without ID |
Classification Frameworks
Not applicable.
Laboratory Notes
- Protect CSF volume for antigen and culture
- Hedge CrAg platforms and cutoffs as local
- Never include antifungal treatment or dosing
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
Common questions about using this Cryptococcus foundational topics Medical Laboratory Library reference in Medical Laboratory Science education.
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