The ova and parasite (O&P) exam is used to help diagnose the cause of prolonged diarrhea. It is ordered to determine whether there are parasites present in the lower digestive tract and, if so, to identify them. Since there are many other causes of diarrhea, the O&P is often ordered along with other tests, such as a stool culture, which identifies the presence of disease-causing bacteria in the stool.
O&P tests may also be ordered to monitor the effectiveness of treatment for a parasitic infection.
Other tests may be used in conjunction with an O&P to help make a diagnosis. A doctor may order a Giardia, Cryptosporidium, or Entamoeba histolyticaantigen test if he suspects that one of these parasites may be causing the diarrhea. These tests detect protein structures on the parasites and can identify an infection, even if no actual parasites or ova are seen in the stool. Since antigen tests only detect a few specific parasites, they are not replacements for the complete O&P, which will detect a wider variety of parasites.
It may be ordered when a person has these symptoms and has recently consumed stream or lake water, been exposed to someone who has a parasitic infection (like a family member), or has traveled outside of the U.S.
O&P tests may also be ordered when someone has been diagnosed with a parasitic infection to monitor the effectiveness of treatment.
If there are no ova or parasites seen, then the diarrhea may be due to another cause. There may also be too few parasites to detect in the sample tested. A doctor may want to order additional O&P tests to confirm this finding and/or may order other tests to search for the cause of the persistent symptoms.
If a parasite is identified, then the person does have a parasitic infection. Ova and parasites present in the stool samples are identified and counted. Numbers may range from many to very few or rare.
Typically a person will only have one type of parasite that is causing their symptoms, but there could be more than one. The most common and frequently detected parasites in the U.S. are:
Entamoeba histolytica (causes amebiasis)
Some examples of other intestinal parasites that may be detected with an O&P include the following.
Single cell parasites:
Roundworms such as Ascaris, Strongyloides
Tapeworms such as Hymenolepis nana, Taenia solium and Diphyllobthrium latum
Flatworms and flukes such as Fasciolopsis buski
The type and duration of treatment will depend on what kinds of parasite(s) are found and on the person's general state of health. The number of parasites seen may give the doctor general information about how heavy or extensive the infection is.
Drug therapies are usually used to treat Giardia, E. histolytica and Cryptosporidium infections. They may resolve themselves after several weeks, but they may also cycle, with symptoms subsiding and then worsening again. In those with healthy immune systems, crypto generally goes away after a few weeks. In those with weakened immune systems (such as those with HIV/AIDS, organ transplant, cancer, etc.), however, crypto may be dangerous, becoming chronic and causing wasting and malnutrition.
This article was last reviewed on August 30, 2011. | This article was last modified on March 4, 2015.
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