As the name suggests, this test is conducted for the detection and identification of parasitic protozoa and also the eggs and larvae of parasitic helminths (worms). This is the reason why it is also called O & P or OAP (Ova and Parasites) or also as stool test. This is usually done on a stool sample and helps diagnose help diagnose infections of the digestive system like the gastrointestinal, GI tract, etc. At times, this is used along with a few other tests like gastrointestinal (GI) pathogens panel or a stool culture, to arrive at an accurate diagnosis.
In this test, the patient is expected to collect his stool or fecal sample and provide it for the test. No special preparation other than informing the doctor about the administration of barium, bismuth, kaolin, magnesia, castor oil or mineral oil is needed for this test. These things may interfere with the identification of protozoa and hence this precaution is needed.
A variety of parasites, including protozoa and helminths may be found. These help in the determination of the infection, which at times may be asymptomatic. At times, the infection may be accompanied by diarrhea, stomach or abdominal pain, etc. The test results are either positive for the presence of the organism that has been identified or negative, indicating no presence. The most prevalent parasites in stool specimens are Giardia intestinalis and Cryptosporidium species, both of which may cause, diarrhea.
The other commonly found parasite is Entamoeba histolytica, which only causes issues in 10 to 20% of the people in which its presence is found. Single cell parasites like Dientamoeba fragilis, Balantidium coli, Cyclospora cayetanensis are also reported. Worms like roundworms, hookworms, tapeworms and flatworms are also found. More tests or clinical examination may be required to diagnose the actual infection as the certain organisms, even if present, are harmless and do not cause any issues.
Usually some special kits are used for this and proper instruction provided on the same needs to be followed. The specimen should be placed in the preservative within half an hour of collection of the sample as per the instructions. The minimum volume of the specimen should be 5 ml. Also, this may have to be repeated for a few days, amounting to at least 3 specimens, due to the irregular nature of the parasite shedding.