Overview
Stool parasitology examination is the laboratory process of macroscopic inspection, direct microscopy, and often permanent staining (± concentration) to detect intestinal protozoa and helminth stages in feces.
Classification
| Prep | Best for | Limitation |
|---|---|---|
| Saline wet mount | Motile trophozoites; eggs/larvae cues | Limited nuclear detail |
| Iodine wet mount | Cyst internal highlights | Kills motility |
| Permanent stain | Protozoan ID criteria | Slower; stain skill required |
| Concentrate (see Lesson 12) | Low-load eggs/cysts | May distort/destroy trophozoites |
Morphologic Features
Report organisms with stage when possible (cyst, trophozoite, egg, larva). Size, shape, nuclei, chromatoid bodies, opercula, and larval features distinguish true parasites from yeast, pollen, and vegetable cells.
Laboratory Characteristics
- Thin, evenly spread wet mounts
- Systematic low-power scan before high-power detail
- Stain QC and known-positive review when available
- Correlate consistency with expected stage
Reference Intervals
O&P series number, preservative kits, stain choice (trichrome vs iron hematoxylin), and antigen/NAAT reflex menus are institutional, verify SOP and package inserts.
Clinical and Laboratory Significance
Positive morphology under adequate methods supports intestinal parasitosis frameworks. Negative exams exclude only what the performed methods could detect given specimen quality and organism load.
Differential Considerations
Differentiate yeast vs cysts, white cells vs amebae, plant spirals vs helminth structures, and Charcot-Leyden crystals (eosinophil breakdown cue) from diagnostic parasite stages.
Comparison Tables
Artifact vs parasite cues
| Finding | Supports parasite call | Suggests artifact |
|---|---|---|
| Round refractile body | Internal nuclei / Giardia features | Budding yeast; empty spheres |
| Motile form | Directional trophozoite motility | Brownian debris motion |
| Egg-like object | Shell + contents criteria | Pollen / vegetable cell |
Classification Frameworks
Not applicable.
Laboratory Notes
- Do not finalize protozoan species from wet mount alone when stain is indicated
- Hedge kits, stains, and series schedules as local
- Never include antiparasitic 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
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