Questions and Answers
What can complicate the gross and microscopic examination of stool specimens?
Free-living organisms found in stool do not lead to confusion in specimen analysis.
False
Name one type of cell that may mimic pathogenic protozoa in stool specimens.
PMNs (Polymorphonuclear leukocytes)
Improper collection techniques can lead to contamination of stool specimens with __________ organisms.
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Match the following artifacts with their resemblance:
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What are the recommended number of stool specimens for adequate parasite detection?
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Urine contamination can help preserve parasites in stool samples.
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What is the acceptable stool sample amount required for a parasite study?
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Trophozoites and cysts are forms of ___ that can be recovered from stool samples.
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Which of the following substances may interfere with the detection of parasites in stool specimens?
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Match the following forms found in stool specimens with their classification:
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What is the ideal condition for a stool specimen to be used for parasitic examination?
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Toilet paper in the stool specimen can help in the examination of parasites.
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Up to six stool specimens can be collected to diagnose amebiasis within 14 days.
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How long should one wait to collect stool specimens after taking antiprotozoal or antihelminthic medications?
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What should be done if a fecal specimen cannot be processed immediately?
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The recommended fixative to stool ratio for successful recovery of parasites is __ parts fixative to one part stool.
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Match the following fixatives with their primary use:
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Which of the following should not be included in a stool sample collection instructions?
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Free-living protozoa and nematodes are typically mistaken for human parasites.
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What is one consequence of not using the correct preservative for stool specimens?
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Study Notes
Examination of Stool Specimens
- Gross and microscopic stool examination can be complicated by artifacts that resemble parasitic forms.
- Artifacts may arise from daily consumption of various vegetable and meat products.
- Human origin cells can mimic pathogenic protozoa, leading to misleading results.
- Spurious infections can occur from ingesting contaminated or infected meats.
- Improper collection techniques can lead to contamination with extraneous organisms.
- Free-living organisms can confound results due to stool contact with water, sewage, or soil.
Artifacts Resembling Parasites
- PMNs can resemble Entamoeba histolytica/E. dispar cysts.
- Macrophages may be mistaken for E. histolytica/E. discreta.
- Stool should not be retrieved from toilet bowl water due to potential contamination with free-living protozoa and nematodes.
- Toilet paper can mask the presence of parasites in stool samples.
Collection Procedures
- Use a clean, dry, leak-proof container without preservatives, and collect approximately 5 g of feces.
- Close the container immediately after collection to avoid contamination.
- Label the specimen with the patient's name, identification number, physician’s name, and date/time of collection.
- Transfer the specimen to the laboratory promptly for analysis.
Preservation of Stool Specimens
- Freshly collected stool samples are ideal for parasitic examination.
- If immediate processing is not possible, specimens should be placed in appropriate preservatives.
- Fixatives preserve protozoa morphology and prevent further development of certain helminth eggs and larvae.
- Recommended fixative-to-stool ratio is three parts fixative to one part stool.
Common Fixatives
- Formalin: All-purpose fixative for helminth eggs, larvae, and protozoan cysts.
- Modified Polyvinyl Alcohol (PVA): Copper or zinc versions may be used.
- Sodium Acetate Acetic Acid Formalin (SAF): Another option for specimen preservation.
- Merthiolate Iodine Formalin (MIF): Used for enhancing specimen quality.
- Schaudinn’s Fixative: Known for preserving detailed morphology.
Detection of Parasites
- Morphological forms of protozoa and helminthes can be detected from well-collected and prepared stool specimens.
- Protozoan stages (trophozoites and cysts) and helminth stages (eggs, larvae, segments, and adult worms) may be present.
- Intermittent shedding of parasites necessitates collection of multiple specimens for accurate detection.
- Protocol typically involves collecting three specimens every other day within 10 days; exceptions are noted for amebiasis diagnosis.
Precautions for Sample Collection
- Always use gloves and a protective coat when handling specimens.
- Certain medications (antacids, barium) can interfere with parasite detection; these effects may take days to clear.
- Delay specimen collection for two weeks after antiprotozoal or antihelminth therapy.
- Use a clean, watertight container with a tight-fitting lid.
- Acceptable stool amount for parasite study is 2 to 5 g (size of a walnut).
- Urine contamination must be avoided, as it can destroy some parasites.
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Description
This quiz focuses on the complexities of gross and microscopic stool examination, specifically the confusing presence of artifacts that may mimic parasitic organisms. It highlights how common dietary items can create misleading results and the potential for spurious infections related to food consumption.
