American Society for Clinical Laboratory Science

View all recommendations from this society

Released June 10, 2020

Do not order a comprehensive stool ova and parasite (O&P) microscopic exam on patients presenting with diarrhea less than seven days’ duration who have no immunodeficiency or no history of living in or traveling to endemic areas where gastrointestinal parasitic infections are prevalent. If symptoms of infectious diarrhea persist for seven days or longer, start with molecular or antigen testing and next consider a full O&P microscopic exam if other testing is negative.

The comprehensive O&P microscopic exam often requires submission of multiple stool samples, it is labor intensive, requires significant expertise to perform, and typically has lower sensitivity when compared to many other tests now available. Instead, consider ordering antigen detection tests (i.e. direct fluorescent antibody, enzyme immunoassay, indirect immunofluorescence assay, rapid immunochromatographic tests), modified acid-fast stain, or molecular tests that detect specific gastrointestinal parasites most commonly acquired in the U.S. When investigating cases of gastrointestinal disease, it is important to take a comprehensive clinical history that considers the patient’s exposure risk, mechanism(s) of transmission, and immune status. Patients lacking international travel history or residence in areas where parasites are endemic are most likely to be exposed to intestinal parasites associated with outbreaks from exposure to contaminated food or water. In the U.S. these pathogens include Giardia duoedenalis (G. lamblia, G. intestinalis), Entamoeba histolytica, Cryptosporidium, and Cyclospora. For most individuals with healthy immune systems, symptoms self-resolve without treatment. In individuals with prolonged symptoms, risk for development of severe infection, or when pathogen identification is necessary for public health reasons, testing is recommended. Numerous antigen detection assays and molecular tests, including multiplex panels, have been developed for targeted detection of the most common gastrointestinal parasites acquired in the U.S.

These items are provided solely for informational purposes and are not intended as a substitute for consultation with a medical professional. Patients with any specific questions about the items on this list or their individual situation should consult their physician.

How The List Was Created

George Fritsma, MS, MLS (ASCP), and the late Cindy Johns, MS, MLS (ASCP) hosted a plenary presentation “Enhancing Laboratory Communication to Reduce Extra-analytical Errors” at the ASCLS Clinical Laboratory Educators’ Conference in Boston in February 2017. Their talk referenced the ABIMF Choosing Wisely initiative. Subsequent discussions resulted in the ASCLS Board of Directors appointing a Choosing Wisely task force that evolved to a standing committee. The committee is composed of ASCLS members representing all medical laboratory science disciplines.

The committee collaborated with respective ASCLS Scientific Assemblies in developing and reviewing recommendations, which the Board of Directors reviewed and accepted for publication. The recommendations were subsequently reviewed in collaboration with the ASCP Test Utilization Steering Committee prior to submission.



American Society for Clinical Laboratory Science (ASCLS) recommendations were developed under the leadership of ASCLS’s Choosing Wisely Committee and the ASCLS president and executive vice president. The Committee examined numerous options based on evidence available through an extensive review of  the literature and member proposals. Subject matter experts from the ASCLS Scientific Assemblies reviewed and recommended approval of their respective recommendations, which are subsequently approved by the ASCLS Board of Directors. The recommendations were subsequently reviewed in collaboration with the ASCP Test Utilization Steering Committee prior to submission.


Centers for Disease Control and Prevention. DPDx- Laboratory identification of parasites of public health concern. Stool specimens- detection of parasite antigens. Website accessed 23 May 2019.

Centers for Disease Control and Prevention. Parasites. Website accessed 23 May 2019.

Garcia LS, et al. Laboratory diagnosis of parasites from the gastrointestinal tract. Clin Microbiol Rev. 2017; 31 doi: 10.1128/CMR.00025-17

Shane AL, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017;65:1963-73. Doi: 10.1093/cid/cix959.