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Ova and Parasite (O&P) Examinations

Introduction | Macroscopic | Microscopic |

Microscopic Examination - Ova and Parasite Examination

Introduction | Direct Wet Smear | Concentration | Permanent Stained Smear

Introduction

The microscopic examination of the stool specimen, normally called the ova and parasite examination, consists of three separate methods: the direct wet smear (trophozoite motility), the concentration (recover more organisms), and the permanent stained smear (demonstrate detailed parasite morphology). Each of these methods is designed for a particular purpose and forms an integral part of the total examination.

Many laboratories receive preserved specimens from both inpatients and outpatients. Because the preserved organisms will no longer exhibit motility, the direct wet smear is no longer considered a mandatory part of the routine ova and parasite examination (on preserved specimens). However, if fresh fecal specimens are delivered to the laboratory, then the direct wet smear, particularly on liquid stools, should be performed. It is NOT necessary to perform a direct wet smear on fresh formed specimens.

In addition to normal specimen debris, the microscopic examination of fecal material may reveal the following:

  1. Trophozoites and cysts of intestinal protozoa.
  2. Oocysts of coccidia and spores of microsporidia.
  3. Helminth eggs and larva.
  4. Red blood cells (RBCs) which may indicate ulceration or other hemorrhagic problems.
  5. White blood cells (WBCs), specifically polymorphonuclear leukocytes (PMNs), which may indicate inflammation.
  6. WBCs (eosinophils) which usually indicate the presence of an immune response (which may or may not be related to a parasitic infection).
  7. Macrophages which may be present in bacterial or parasitic infections.
  8. Charcot-Leyden crystals which may be found when disintegrating eosinophils are present (may or may not be related to a parasitic infection).
  9. Fungi (Candida spp.) and other yeasts and yeastlike fungi.
  10. Plant cells, pollen grains, or fungal spores which may resemble some helminth eggs, protozoan cysts, coccidian oocysts, or microsporidial spores.
  11. Plant fibers or root hairs or animal hairs which may resemble helminth larvae.