What are procedures for stool specimen exam in the evaluation of cryptosporidiosis?

Updated: Nov 11, 2019
  • Author: Melinda B Tanabe, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Concentrated sediment of fresh (within 30 min after passage of stools) or formalin-preserved stool may be used. Other types of clinical specimens, such as duodenal fluid, bile, and pulmonary samples (induced sputum, bronchial wash, biopsies) may also be stained.

The formalin ethyl acetate method is used to concentrate stool before staining with a modified acid-fast stain, because routine laboratory examination of stool for ova and parasites does not detect Cryptosporidium. [1] This technique allows for differentiation from fecal debris or yeast, which stains blue or green, versus oocysts, which counterstain pink or red. Careful examination of slides is imperative, as oocysts can easily be missed.

Because shedding may be intermittent, examine at least 3 stool specimens collected on separate days before considering the test results negative. Fecal leukocytes are not found in stool specimens, because invasion does not occur below the epithelial layer of the mucosa.

Other testing strategies include the following:

  • GI biopsy specimens can be used instead of stool specimens; a high concentration of oocysts is seen in the jejunum.
  • Electron microscopy of stool or biopsy specimens can also be performed for direct visualization of oocysts.
  • PCR and immunohistochemistry can be used on tissue samples, precluding the need for staining. [45]
  • Serologic detection of specific anti- Cryptosporidium antibodies is primarily used as a research or epidemiologic tool.

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