Diagnosis of Intestinal Parasites

Quest Diagnostics offers O&P testing in accordance with guidelines set forth by the Clinical Laboratory Standards Institute (CLSI) and in concert with best practices published in various American Society of Microbiology (ASM) press books for optimizing the collection, testing, and reporting of human parasitic pathogens.^1-4 O&P exams may detect trophozoites and/or cysts of important human parasitic pathogens including Cryptosporidium sp, Coccidia sp, Entamoeba histolytica, E histolytica/dispar, Giardia sp, Isospora sp, Microsporidia sp, Schistosoma mansoni, and Schistosoma haematobium, as well as non-pathogenic parasites that indicate exposure to unclean environmental sources.

Yes. Recommended testing can vary depending on symptoms, travel history, and geographic prevalence of disease. Table 2 provides guidance on this topic based upon ASM and IDSA recommendations. 

Parasites may only be shed intermittently and 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.^2-3 For patients without diarrhea, 2 of the specimens should be collected after normal movements, and 1 after a cathartic, such as magnesium sulfate. If the patient has diarrhea, laxatives should not be used. Submission of more than 1 specimen collected on the same day usually does not increase the sensitivity of the test.^2-4,6

For Giardia antigen testing, testing of specimens collected on 2 different days is recommended to improve sensitivity.⁶

Preferred transport media for stool O&P exams include either a single vial of Total-Fix or paired vials of 10% formalin and PVA. These transport media have met verification and validation criteria for reliability with respect to our specific human parasitic pathogen testing methodologies.^7-14

We do not accept Ecofix, Protofix, SAF, or any other preservatives outside of those mentioned above. Any transport media besides those listed as “acceptable” above have either not been validated or did not pass validation criteria for use with our specific testing methodologies.⁷

Data suggest that for patients who have been hospitalized for more than 3 days, diarrhea is generally the result of non-parasitic causes.²

Urine is acceptable for the detection of Schistosoma haematobium. Urine should be collected around noon and 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 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.

The Centers for Disease Control and Prevention recommends the additional non-stool sources listed below.¹³ Note that testing of these specimens may require approval of the Quest Diagnostics Medical Director.

• Duodenal aspirates should be submitted in Total-Fix or 10% formalin for examination when Giardia duodenalis or Strongyloides stercoralis are suspected.
• Sigmoidoscopy material and abscesses of the liver and lung should be submitted in Total-Fix or PVA when Entamoeba histolytica is suspected.