Stool Wet Mount Microscopy


1. Objective

To detect motile trophozoites, cysts, ova, or larvae of intestinal parasites (protozoa and helminths) in a fresh stool sample using light microscopy.

2. Principle

In wet mount microscopy, a small amount of stool is mixed with a drop of saline or iodine on a glass slide and covered with a coverslip.

  • Saline (0.85% NaCl) allows observation of motile trophozoites and helminth larvae.

  • Iodine (e.g., Lugol’s iodine) stains protozoan cysts, enhancing visibility of nuclear structures.

Microscopy is used under low (10x) and high power (40x) objectives to identify parasites based on morphology and motility.

3. Materials

  • Fresh stool sample

  • Clean glass slides and coverslips

  • Normal saline (0.85% NaCl solution)

  • Iodine solution (Lugol’s iodine)

  • Applicator sticks or toothpicks

  • Dropper or pipette

  • Light microscope (10x and 40x objectives)

  • Gloves and PPE

  • Biohazard waste container

4. Procedure

  • Place a small drop of saline on one side and iodine on the other side of a clean slide.

  • Mix a small amount of stool (pea-sized) with each drop using an applicator stick.

  • Cover with coverslip, avoiding air bubbles.

  • Examine under microscope:

    • First under 10x for scanning.

    • Then under 40x to observe fine details.

  • Look for trophozoites, cysts, ova, and larvae based on size, shape, and internal structures.

5. Result

  • Positive: Identification of one or more types of intestinal parasites:

    • Entamoeba histolytica trophozoites

    • Giardia lamblia cysts or trophozoites

    • Helminth eggs (e.g., Ascaris, Hookworm, Trichuris)

  • Negative: No parasites detected

6. Uses

  • Rapid screening test in clinical laboratories

  • Common in diagnosing intestinal parasitic infections

  • Helps distinguish motile forms (trophozoites) and cystic stages

  • Essential in outbreak investigations of parasitic diseases

7. Conclusion

Stool wet mount microscopy is a simple, cost-effective, and rapid method for detecting intestinal parasites. However, its sensitivity can vary, and it may miss low-burden infections—so it’s often complemented with concentration techniques or antigen-based tests.

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