Test Catalog

Test ID: OAP    
Ova and Parasite, Concentrate and Permanent Smear, Microscopy, Feces

Useful For Suggests clinical disorders or settings where the test may be helpful

Detection and identification of parasitic protozoa and the eggs and larvae of parasitic helminths

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

A variety of different parasites may be found in stool specimens, duodenal aspirates, and other intestinal specimens. These parasites may include protozoa (microscopic unicellular eukaryotes) and helminths (aka worms). Infection is often asymptomatic, but symptoms range from diarrhea and malnutrition, intestinal obstruction, and rarely, death.


The most common intestinal reported parasites in stool specimens are Giardia intestinalis (aka Giardia duodenalis, Giardia lamblia) and Cryptosporidium species. Both parasites may cause watery diarrhea and are endemic in the United States. The best tests for these 2 common parasites are parasite-specific fecal antigen tests (GIAR / Giardia Antigen, Feces and CRYPS / Cryptosporidium Antigen, Feces).


Other parasites are less commonly seen in the United States, and the stool parasitic exam is the appropriate test for their detection. See Parasitic Investigation of Stool Specimens Algorithm in Special Instructions for determining which test should be ordered based on the patient's exposure history and risk factors. If evaluating a patient for diarrhea, see Laboratory Testing for Infectious Causes of Diarrhea Algorithm.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


If positive, organism identified

Interpretation Provides information to assist in interpretation of the test results

A positive result indicates the presence of the parasite but does not necessarily indicate that it is the cause of any symptoms. Some strains of protozoa are nonpathogenic and some helminths cause little or no illness.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

If possible adult worms or proglottids are identified in stool or the patient’s undergarments, they should be placed in 70% alcohol and submitted for PARID / Parasite Identification.


For optimal results, the specific test should be ordered for detection of Giardia, Cryptosporidium, microsporidia, Cyclospora, or pinworm. The OAP / Parasitic Examination is not the optimal method for detecting these parasites.


Parasitic examination of a minimum of 3 stool specimens is indicated for detecting most intestinal protozoa and helminths with maximum sensitivity.


Parasitic infections are uncommonly acquired in the hospital setting. This test is not usually useful in patients hospitalized for more than 3 days.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Garcia L: Diagnostic Medical Parasitology. Fifth edition. Washington, DC, ASM Press, 2007

Special Instructions Library of PDFs including pertinent information and forms related to the test