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Stool Test: Giardia Antigen

What It Is

The Giardia lamblia parasite is one of the chief causes of diarrhea in the United States. It lives in the gastrointestinal (GI) system and passes from the body in stool (feces).

In a Giardia antigen test, a stool sample is checked for the presence of Giardia.

Why It's Done

The Giardia antigen test is used to make a diagnosis of giardiasis, the digestive tract illness caused by Giardia lamblia. A doctor may order the test if your child has symptoms such as watery diarrhea, abdominal pain, large amounts of intestinal gas, appetite loss, and nausea or vomiting, especially if there's been an outbreak of giardiasis at your child's school or daycare center, your child recently drank untreated water, or if your family recently visited a developing country. The test also may be used to determine if treatment for giardiasis has been effective.

The test may be ordered by itself or in combination with an ova and parasite exam (a microscopic evaluation of stool for the presence of parasites). The antigen test is more sensitive in detecting Giardia lamblia than the ova and parasite (O&P) exam, but it can't identify any other organisms or conditions that cause gastrointestinal distress.


Unlike most other lab tests, a stool sample is often collected by parents at home, not by health care professionals at a hospital or clinic.

If possible, your child may be asked to avoid certain foods and treatments for 2 weeks before the test, including:

  • antidiarrheal drugs
  • antibiotics and antiparasite drugs
  • enemas


The doctor or hospital laboratory will usually provide written instructions on how to collect a stool sample. If instructions aren't provided, here are tips for collecting a stool sample from your child:

  • Be sure to wear latex gloves and wash your hands and your child's hands afterward.
  • Many kids with diarrhea, especially young kids, can't always let a parent know in advance when a bowel movement is coming. So a hat-shaped plastic lid is used to collect the stool specimen. This catching device can be quickly placed over a toilet bowl, or under your child's bottom, to collect the sample. Using a catching device can prevent contamination of the stool by water and dirt. Another way to collect a stool sample is to loosely place plastic wrap over the seat of the toilet. Then place the stool sample in a clean, sealable container before taking it to the lab.
  • Plastic wrap can also be used to line the diaper of an infant or toddler who isn't yet using the toilet. The wrap should be placed so that urine runs into the diaper, not the wrap.
  • Your child shouldn't urinate into the container and, if possible, should empty his or her bladder before the bowel movement so the stool sample isn't diluted by urine.
  • The stool should be collected into a clean, dry plastic jar with a screw-cap lid. For best results, the stool should be brought to the lab right away. If this isn't possible, the stool should be stored in preservative provided by the lab and then taken there as soon as possible.

What to Expect

After the sample arrives at the laboratory, a technician puts a stool sample in contact with a chemical that changes color in the presence of products of the Giardia lamblia parasite. It's important to remember that the Gardia antigen test detects the presence of only that specific parasite, so the doctor may order additional tests to reach a definitive diagnosis.

Getting the Results

In general, the result of the Giardia antigen test is reported within a day.


No risks are associated with collecting stool samples.

Helping Your Child

Collecting a stool sample is painless. Tell your child that collecting the stool won't hurt, but it has to be done carefully. A child who's old enough might be able to collect the sample alone to avoid embarrassment. Tell your child how to do this properly.

If You Have Questions

If you have questions about the Giardia antigen test, speak with your doctor.