Diagnosis of Intestinal Parasites

O&P exams may detect trophozoites and/or cysts of important human parasitic pathogens including Cryptosporidium species, Coccidia species, Entamoeba histolytica, E. histolytica/dispar, Giardia species, Isospora species, Microsporidia species, Schistosoma mansoni, and Schistosoma haematobium as well as non-pathogenic parasites that indicate exposure to unclean environmental sources. However, the accuracy of a single specimen submitted for O&P exam is only 75.9%.⁵

The preferred transport media for stool O&P exams are either a single vial of Total-Fix^® or paired vials of 10% formalin and PVA containing 10 g or 10 mL (minimum of 5 g or 5 mL) of stool; specimens should be transported at room temperature. These transport media have met verification and validation criteria for reliability with respect to our specific human parasitic pathogen testing methodologies. ^1,3,4,6,7

Test performance depends on the transport media used.^8,9 We do not accept Ecofix, Protofix, SAF, or any other preservatives outside of those mentioned above. Any transport media other than those listed as “acceptable” in Question 3 have either not been validated or did not pass validation criteria for use with our specific testing methodologies.

Data suggest that for patients who have been hospitalized for more than 3 days, diarrhea is generally the result of nonparasitic causes.¹

Parasites may only be shed intermittently; thus, repeat testing may be necessary for detection. For routine examination for parasites before treatment, a minimum of 3 specimens, collected on alternate days, is recommended.^1,3,6 For patients without diarrhea, collect 2 of the specimens after normal bowel movements and 1 after a cathartic, such as magnesium sulfate. If the patient has diarrhea, do not use laxatives. Submitting more than 1 specimen collected on the same day usually does not increase the sensitivity of the test.^1,3,4

Urine is acceptable for the detection of Schistosoma haematobium. Urine should be collected around noon, submitted in a sterile, leak-proof container, and transported refrigerated to the laboratory as soon as possible.

Sputum or bronchoalveolar lavage may be submitted in Total-Fix^®, 10% formalin, or unpreserved for examination when Paragonimus westermani eggs, Strongyloides stercoralis larvae, Ascaris lumbricoides larvae, or hookworm larvae are suspected. Unpreserved specimens should be refrigerated and transported to the laboratory as soon as possible.

If a worm is visible in the patient sample, submit a worm in alcohol in a leak-proof container for Parasite Identification, Worm (test code 3950). Do NOT order an O&P exam or submit in Total-Fix^® or other stool preservative.

The Pinworm Exam (test code 4496) is the recommended test for detection of Enterobius vermicularis (pinworm). A special collection device called a pinworm paddle is available from Client Supplies for perianal material collection. Alternatively, clear cellulose tape applied to a clear glass slide is appropriate for submission. E. vermicularis most often infects children and is associated with perineal pruritus.