Stool for Blastocystis hominis

                                  


1. Objective

To detect Blastocystis hominis in stool specimens using microscopic, culture, or molecular methods, aiding in the diagnosis of blastocystosis.

2. Principle

Blastocystis hominis is an intestinal protozoan with variable forms (vacuolar, granular, amoeboid). Diagnosis is made by detecting characteristic vacuolated forms in stool through:

  • Direct wet mount microscopy

  • Stool concentration techniques

  • Permanent staining (e.g., trichrome)

  • Culture in Jones' medium (for research/lab confirmation)

  • PCR (for species-level identification)

3. Materials

  • Fresh stool specimen

  • Saline and Lugol’s iodine

  • Glass slides and coverslips

  • Formalin-ether for concentration

  • Trichrome stain (optional)

  • Culture media (optional)

  • Microscope

  • PPE and waste disposal supplies

4. Procedure

A. Direct Wet Mount

  1. Mix stool sample with saline and prepare a wet mount.

  1. Examine under 10x and 40x magnification.

  2. Identify vacuolated forms (~5–30 µm), round/oval with a central body and peripheral cytoplasm.

B. Formalin-Ether Concentration

  1. Mix stool with formalin, filter, and centrifuge with ether.

  2. Examine sediment microscopically for Blastocystis forms.

C. Staining (Trichrome)

  1. Fix a thin stool smear on a slide.

  1. Stain with trichrome and examine under oil immersion.

  2. Look for blue-green central vacuole with red cytoplasm.

5. Result Interpretation

  • Positive: Observation of Blastocystis hominis in any morphological stage.

  • Negative: No forms seen—repeat testing or molecular assay may be necessary.

6. Uses

  • Diagnose blastocystosis, especially in patients with chronic or unexplained diarrhea.

  • Differentiate from other protozoal infections.

  • Often reported as commensal, but may be pathogenic in immunocompromised individuals or symptomatic hosts.

7. Conclusion

Stool examination for Blastocystis hominis is useful in investigating gastrointestinal complaints, especially when other pathogens are ruled out. Though sometimes controversial, its detection is relevant in clinical parasitology, and confirmation via concentration or staining enhances accuracy.

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