What Is a Stool Ova and Parasite Test (O&P)?

Medically Reviewed by Minesh Khatri, MD on September 11, 2023
4 min read

A stool ova and parasite, or O&P, test is a simple way of diagnosing parasite infections. This test determines whether parasites and their eggs are present in your stool.

The stool O&P test is a common way to find out if you have parasites in your digestive tract.

Parasites are organisms that live in or on you and get their food from your body. They're often in your digestive tract and can cause diseases. Parasites are more common in countries that lack proper sanitation, but despite sanitation measures, lots of people also get parasites, including those living in the United States.

Parasites are spread through stool from people with an infection. You can get parasites from:

  • Touching soil that's contaminated with parasites
  • Eating undercooked or raw meat that has worms
  • Swimming in contaminated lakes or rivers
  • Touching things that someone who has parasites has touched
  • Changing diapers or helping children who have parasites

Your doctor might order a stool parasite test for you or your child if you have any symptoms of a parasite infection. These include:

  • Diarrhea
  • Bloating
  • Nausea, or feeling sick
  • Stomach cramping
  • Greasy stools that float
  • Unintentional weight loss
  • Gas
  • Dehydration 
  • Fever
  • Bloody stool
  • Mucus in your stool
  • Itchy rectum

Some of the most common parasitic infections are Giardia, cryptosporidium, and pinworms. Pinworms are common in children and can cause an itchy rectum, which is usually worse at night. Children can get pinworms from daycare and school.

Your doctor might also order this test if you have these symptoms and have traveled recently. If your test results are positive, your doctor might ask you to do more stool tests to check how well the treatment is working.

Your doctor or lab will send you home with a collection bottle and a toilet pan. The bottle often has a type of spoon attached to the lid that helps you collect stool.

To collect a sample:‌

  1. Place the pan in your toilet and use the washroom as normal. If they didn’t give you a pan, you can tape a plastic bag to the toilet. 
  2. Put on rubber gloves and collect a sample as directed. Make sure there's no urine, water, toilet paper, or wipes in the sample.  
  3. Seal the container and label it.
  4. Empty the pan and discard it and your gloves.
  5. Wash your hands. 

If you need to collect a sample from your baby or toddler in diapers, line the diaper with a plastic bag and follow the other collection steps. Try to get the bag so that urine doesn’t mix with the stool. 

You will need to take your sample to the lab as soon as possible. If you can’t get there right away, refrigerate your sample. The collection bottle usually comes in a plastic bag that you can seal it in. 

Sometimes your doctor might want you to take a few samples, so you will need to repeat the process and bring all the samples into the lab. 

If your test comes back positive, this means the lab found parasites, parasite eggs, or both. If these are present, it means you have an infection.

A negative test means they didn’t find any eggs or parasites. This can mean you don’t have an infection, or it can mean there isn’t enough to find. The stool tests have better accuracy when more samples are examined, which is why you might have to do a few collections. 

Some medications can affect your results for up to one week after you stop taking them. These include:

  • Bismuth
  • Barium
  • Oily laxatives
  • Antacids
  • Antibiotics
  • Some diarrhea medications

You might need to stop taking these medications before doing the test to make sure it’s accurate, but you should only do this if your doctor tells you. Make sure to discuss any other over-the-counter medications or herbs and vitamins you’re taking.

If you or your child have an itchy rectum, your doctor might also have you do a tape test. This test requires you to place the sticky side of a piece of tape to the skin around your anus just before bedtime to collect any pinworm eggs while you sleep. The lab will then put the piece of tape under a microscope to look for eggs.

If you're still experiencing digestive symptoms after providing multiple samples with an O&P test that came back negative, your doctor may decide to perform a colonoscopy. This is a test where they insert a thin tube with a camera into your rectum and large intestine to view your lower gastrointestinal tract. This can help them find any other problems. 

There are no risks related to this stool test. The laboratory only needs some of your stool to conduct it, so there's no discomfort.

If you have digestive symptoms and think you need this test, make sure to talk to your doctor.