What it is: An ova and parasite (O&P) exam is a microscopic examination of stool, in which a lab professional looks for parasites and their eggs (ova) or cysts on stained slides.
Why it's ordered: Typically ordered for persistent or recurrent diarrhea lasting more than 7–10 days, especially after travel to endemic areas, camping, or exposure to untreated water; also used for immunocompromised patients or during daycare/household outbreaks with known parasitic exposure. Often paired with a GI pathogens panel, stool culture, or targeted antigen tests.
What it detects: Helminths (eggs and larvae of roundworms, whipworms, hookworms, tapeworms) and protozoa (cysts/trophozoites of organisms like Giardia and Entamoeba). Some parasites — Cryptosporidium, Cyclospora, Microsporidia — are shed in forms that need separate antigen tests, acid-fast stains, or PCR.
Collection & prep: Usually 2–3 separate stool samples collected on different days, since parasites are shed intermittently and a single sample only catches roughly 60% of infections versus over 95% with three. Samples must avoid contamination with urine or water, and recent barium, antidiarrheals, or antibiotics can interfere with results.
Results:
Positive – parasite(s) identified, with genus/species and life-cycle stage noted
Negative – no parasites seen; doesn't fully rule out infection, particularly if only one sample was tested
Possible complications of parasitic GI infection: Untreated infections can cause chronic diarrhea, malabsorption, and nutrient deficiencies. Because single-sample testing can miss intermittent shedders like Giardia, persistent symptoms after a negative result often warrant repeat O&P testing or a targeted PCR/antigen panel.
Statements made in the Clinical Manual have not been evaluated by the FDA. The products mentioned are not intended to diagnose, treat, cure or prevent any disease.
