# Guideline for the Collection and Testing of Stool Specimens for Ova and Parasites in Symptomatic Patients
Revised May, 2015
The purpose of this guideline is to recommend to physicians which clinical situations warrant a stool sample for ova and parasites (O&P), how to order the test, collect the specimen, interpret the results, and understand the test limitations.
Parasitic infections are exceedingly common worldwide. It has been estimated that nearly 25% of the population in less developed countries harbour the roundworm Ascaris lumbricoides.
The examination of the stool for O&P is the most rewarding test for diagnosis of a parasitic infection because the majority of parasitic infections occur in the bowel.
It is important to recognize that certain chronic parasitic infections from organisms such as, Strongyloides stercoralis, Schistosoma species, and invasive Entamoeba histolytica may compromise a patient's health. Patients suspected of being infected with these organisms warrant extensive parasitological evaluation.

# Clinical Situations that Warrant Requesting a Stool Sample for O&P  Patients with:
- persistent or recurring diarrheal conditions, including patients with bloody diarrhea; o chronic bowel dysfunction or persisting irritable bowel like symptoms, particularly if it can be related to travel or rural residence; o a variety of systemic conditions such as anemia, weight loss, chronic cough, particularly if associated with past ingestion of potentially contaminated food; o eosinophilia and/or serum IgE elevation; o persistent diarrhea with exposure to infants in day care centres (associated with Giardia lamblia, Cryptosporidium parvum); o chronic diarrhea and history of HIV infection or other risk factors causing immunosuppression; o chronic diarrhea and a history of raw fish ingestion.  Symptomatic patients with a history of extended residence in developing areas of the world.  Diarrhea in a man who has sex with a man (MSM). MSM status is associated with Giardia lamblia and Entamoeba histolytica.

# Ordering Instruction
While Giardia lamblia and Cryptosporidium parvum can cause acute diarrhea, over 80% of acute diarrheas are bacterial in etiology. It is important to consider whether the patient is a likely candidate for parasitological testing based on epidemiologic history (e.g., travel, rural water supplies) before automatically ordering O&P. If the epidemiology is pertinent, the diarrhea has persisted for more than several days, and the potential incubation period is at least a week, then do order an O&P test.
DO NOT initially order multiple tests (e.g., do not order x3). More than 90% of parasites can be detected from one appropriately collected, properly preserved single stool specimen. 1 Evidence has demonstrated that ordering multiple specimens is unnecessary for the diagnosis of most protozoal infections. 1,2 If helminthic infections are strongly suspected, more than one specimen for O&P examination may be required due to the intermittency of helminth egg shedding.
If the first specimen is negative and intestinal parasites are still strongly suspected from the clinical condition or there is a significant travel history, resubmit a second and a third specimen collected on separate days. 1, 2

# Collecting Specimens
The patient should be provided with an O&P collection kit that consists of a screw cap jar containing Sodium Acetate-Acetic Acid Formalin (SAF) preservative to stabilize and preserve pathogens en route to the laboratory.
Please refer to an individual laboratory's specimen collection guideline for complete specimen collection directions that should be provided to the patient.
The patient should be advised that if the specimen is not labelled with 2 identifiers it will be discarded e.g. patient's full name and either birth date or OHIP number.

# Limitations 3
Antimicrobials may reduce amoeboid parasitic levels significantly for up to 3 weeks resulting in false negatives.
Specimens contaminated with water or urine may yield false negative results, as water or urine may have lysed any trophozoites that were present.
Where possible, avoid ordering O&P examination for 10 days after a patient has had barium studies, bismuth, antacids, mineral oil, anti-malarials, non-absorbable anti-diarrheal preparations, or recent mineral laxatives.
Improper collection may result in extraneous organisms and artifacts resembling cysts and eggs.
It may take 3 to 5 days to generate a report due to the labor intensive nature of the examination process. For the rare instances where processing must be expedited, a telephone request must be made to the laboratory's microbiologist. Treatment is indicated for the majority of helminth infections, but in some cases, clinical correlation would also be required (i.e., pregnancy; contraindication to anti-helminthic etc.).

# Additional Tests
Although most intestinal parasites can be identified by examination of preserved stools, some infections may require the collection of other types of specimens, such as peri-rectal/anal swabs (pinworm paddles), duodenal aspirates, or tissue biopsies. Special laboratory techniques may only be performed, if sufficient relevant clinical information is provided to the laboratory.
Enzyme Immunoassays (EIA) & Polymerase Chain Reaction (PCR) assays can be used to screen some stool specimens and for confirmatory testing in some cases (e.g. PCR may be useful for the differentiation of the potentially invasive E. histolytica from the non-invasive species).
These tests must be ordered on a Public Health Ontario Laboratory (PHOL) requisition.
Requisitions and specimen collection instructions for these tests are available on the Public Health Ontario website at /.
The OAML gratefully acknowledges the contribution of the following experts:

# Laboratory Guidelines in Support of Clinical Practice
The OAML, through its Quality Assurance Committee, co-ordinates the development, dissemination, implementation and review of Guidelines for Clinical Laboratory Practice.
Guidelines are reviewed every 5 years, or as the literature warrants. When consensus on the Guideline is achieved by the Committee, the Guideline is submitted to the OAML's Board of Directors for approval before distribution to Clinicians. Warning & Disclaimer This Guideline was prepared to assist clinicians who order tests from community laboratories. Users must ensure that their own practices comply with all specific government policies and specific legislative and accreditation requirements that apply to their organizations. The Guideline is not meant to be construed as legal advice or be all inclusive on this topic. Given the complexity of legal requirements, users are reminded that whenever there is uncertainty regarding whether some aspect of a Guideline is appropriate for their practice or organization, further direction should be obtained from the Laboratory Director, their own professional association, college and/or legal counsel or appropriate government ministry.