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Diagnosis of Intestinal Parasites

Test codes: 681, 1748, 3562, 3950, 4496, 8625, 10018, 34964, 39441, 90389

The ova and parasite (O&P exam) is not recommended as the routine test for diagnosis of intestinal parasites in the United States because the most common intestinal parasites are better detected by other methods.1,2 Recommended testing varies depending on symptoms, travel history, and geographic prevalence of disease.1–4  The Table provides guidance for testing based upon recommendations from the American Society for Microbiology (ASM) and Infectious Diseases Society of America (IDSA). Refer to the Quest Diagnostics Test Directory for specimen collection and transport information.

Table 1. Recommended parasite testing in specific situations

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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.


  1. Garcia LS. Diagnostic Medical Parasitology. 5th ed. American Society for Microbiology; 2007.
  2. Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017;65(12):e45-e80. doi:10.1093/cid/cix669
  3. Shimizu RY, Garcia LS. Specimen Collection, Transport, and Processing: Parasitology. In: Couturier MR, ed. Manual of Clinical Microbiology. 13th ed.; 2021. doi:10.1128/9781555817381.ch133
  4. Couturier MR. Collection and Preservation of Fecal Specimens. In: Pritt BS, Couturier MR, eds. Clinical Microbiology Procedures Handbook. 5th ed.; 2023:11.2.1- doi:10.1128/9781555818814.ch9.2.1
  5. Cartwright CP. Utility of Multiple-Stool-Specimen Ova and Parasite Examinations in a High-Prevalence Setting. J Clin Microbiol. 1999;37(8):2408-2411. doi:10.1128/jcm.37.8.2408-2411.1999
  6. Clinical Laboratory Standards Institute. Procedure for Recovery and Identification of Parasites from the Intestinal Tract; Approved Guideline. CLSI document M28-A2. Published online 2005.
  7. Medical Chemical Corporation. Total-FixTM Stool Collection System. Processing procedure. Published online 2013.
  8. McHardy IH, Wu M, Shimizu-Cohen R, Couturier MR, Humphries RM. Detection of Intestinal Protozoa in the Clinical Laboratory. J Clin Microbiol. 2014;52(3):712-720. doi:10.1128/jcm.02877-13
  9. Fedorko DP, Williams EC, Nelson NA, Calhoun LB, Yan SS. Performance of three enzyme immunoassays and two direct fluorescence assays for detection of Giardia lamblia in stool specimens preserved in ECOFIX. J Clin Microbiol. 2000;38(7):2781-2783. doi:10.1128/jcm.38.7.2781-2783.2000


This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

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