TABLE 2

Approaches to test ordering for stool parasitology

Patient and/or situationTest(s) orderedaFollow-up test(s) ordered
Patient with diarrhea and AIDS or another cause of immune deficiency; potential waterborne outbreak (municipal/city water supply)Cryptosporidium or Giardia/Cryptosporidium immunoassayIf immunoassays are negative and symptoms continue, special tests for microsporidia (modified trichrome stain) and other coccidia (modified acid-fast stain) and an O&P should be performed.
Patient with diarrhea nursery school, day care center, camper backpacker; patient with diarrhea and potential waterborne outbreak (in a resort setting); patient with diarrhea from areas where Giardia is the most common parasite foundGiardia or Giardia/Cryptosporidium immunoassay (perform testing on two stools before reporting the patient as negative) (particularly relevant for areas of the United States where Giardia is the most common organism found)If immunoassays are negative and symptoms continue, special tests for microsporidia and other coccidia (see above) and an O&P should be performed.
Patient with diarrhea and relevant travel history outside the United States; patient with diarrhea who is a past or present resident of a developing country; patient in an area of the United States where parasites other than Giardia are found (large metropolitan areas like Los Angeles, CA, New York, NY, Boston, MA, Miami, FL, etc.)O&P, Entamoeba histolytica/E. dispar immunoassay, immunoassay for confirmation of E. histolytica (various tests for Strongyloides may be relevant [even in the absence of eosinophilia], particularly if there is any history of pneumonia [migrating larvae in the lungs], sepsis, or meningitis [fecal bacteria carried by migrating larvae], including an agar culture plate [the most sensitive diagnostic approach for Strongyloides])The O&P is designed to detect and identify a broad range of parasites (amoebae, flagellates, ciliates, Cystoisospora belli, helminths); if exams are negative and symptoms continue, special tests for coccidia (fecal immunoassays, modified acid-fast stains, autofluorescence) and microsporidia (modified trichrome stains, calcofluor white stains) should be performed. Fluorescent stains are also options.
Patient with unexplained eosinophilia and possible diarrhea; if chronic, the patient may also have a history of respiratory problems (larval migration) and/or sepsis or meningitis (hyperinfection)O&P (recommended, although the agar plate culture for Strongyloides stercoralis [more sensitive than the O&P] is also recommended, particularly if there is any history of pneumonia [migrating larvae in lungs], sepsis, or meningitis [fecal bacteria carried by migrating larvae])If tests are negative and symptoms continue, additional O&Ps and special tests for microsporidia (modified trichrome stains, calcofluor white stains, fluorescent stains) and other coccidia (modified acid-fast stains, autofluorescence, fluorescent stains) should be performed. Serology for Strongyloides may also be recommended.
Patient with diarrhea (from suspected foodborne outbreak)Test for Cyclospora cayetanensis (modified acid-fast stain, autofluorescence, fluorescent stains)If tests are negative and symptoms continue, special procedures for microsporidia and other coccidia and an O&P should be performed.
  • a Depending on the particular immunoassay kit used, tests for various single or multiple organisms may be included. Selection of a particular kit depends on many variables: clinical relevance, cost, ease of performance, training, personnel availability, number of test orders, training of physician clients, sensitivity, specificity, equipment, and time to result, etc. Very few laboratories handle this type of testing in exactly the same way. Many options are clinically relevant and acceptable for good patient care. It is critical that the laboratory report indicate specifically which organisms can be identified using the kit; a negative report should list the organisms relevant to that particular kit. It is important to remember that sensitivity and specificity data for all of these fecal immunoassay kits (fluorescent-antibody assay, enzyme immunoassay, cartridge formats) are comparable.