Skip to content
My WebMD Sign In, Sign Up

Information and Resources

Font Size

Stool Analysis for Giardiasis (Ova and Parasite Test)

A stool sample is collected and analyzed for the presence of the parasite G. lamblia or its cysts. The stool sample may be collected at home, in the doctor's office, or in the hospital.

If the stool is collected at home, it may help to have a bowel movement directly into a plastic bag taped to the toilet seat or into a plastic "hat" provided by your doctor. It is very important to wash your hands after collecting the sample, to avoid spreading a possible infection to others.

Why It Is Done

A stool analysis is done if the medical history and symptoms show that you may have giardiasis. A stool analysis also may be able to find other parasites as well as Giardia lamblia and may be helpful when the diagnosis is unclear.

Results

If a giardia infection is present, the parasite or its cysts can be seen when the stool is looked at under a microscope. Evaluating 3 stool samples detects up to 90% of Giardia lamblia infections.1

If giardiasis is suspected, an antigen test may be done on the stool or a sample of the fluid from the small intestine (duodenal contents). Fluid from the small intestine may be collected by endoscopy. In rare cases, a string test may also be done to look for the parasite.

What To Think About

People may have symptoms before the parasite shows up in their stool. So a single stool sample taken when symptoms first appear often does not contain any parasites. For an accurate diagnosis, most doctors recommend analyzing at least 3 samples, collected on alternate days.

To reduce costs, you may want to wait for the results of the first analysis before doing a second or third test. If Giardia lamblia is found in the first test (positive result), no more tests are needed.

People with chronic giardiasis tend to pass large numbers of the parasite in their stools at about 2-week intervals. If chronic giardiasis is suspected, 3 stool samples may be collected 4 to 7 days apart to maximize the chances of finding the parasite. Stools may also be collected when the person is passing loose (rather than formed) stools. More parasites seem to be passed in loose stools.

Substances that may interfere with test results include:

  • Antacids and antidiarrheals.
  • Antibiotics.
  • Antiparasite drugs.
  • Barium (a contrast material used for X-rays).
  • Enemas or laxatives.

If possible, these products should be avoided for 2 weeks before collecting a stool sample.

Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.

Related Information

Citations

  1. Hill DR, Nash TE (2010). Giardia lamblia. In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Disease, 7th ed., vol. 2, pp. 3527–3534. Philadelphia: Churchill Livingstone Elsevier.

ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerW. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Last RevisedSeptember 9, 2011

WebMD Medical Reference from Healthwise

Last Updated: September 09, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

Hot Topics

WebMD Video: Now Playing

Click here to wach video: Dirty Truth About Hand Washing

Which sex is the worst about washing up? Why is it so important? We’ve got the dirty truth on how and when to wash your hands.

Click here to watch video: Dirty Truth About Hand Washing

Popular Slideshows & Tools on WebMD

feet
Solutions for 19 types.
Woman sitting in front of UV lights
Is yours working?
Healthy breakfast
What are you eating?
Young man exercising on bike
How not to get sick at the gym.
MS Overview
Recognizing symptoms.
bowl of yogurt with heart shape
Eat for a healthy heart.
Woman scrutinizing nose in mirror
Tips that work.
close up of leg with psoriasis rash
Know what to look for.
Woman sitting with child
Do you know the symptoms?
lone star tick
How to identify that bite.
young woman in sun
What to watch for.
Thyroid exam
See how much you know.

Women's Health Newsletter

Find out what women really need.