Stool testing for cysts and parasites: when it is performed, sampling and results

Stool testing for cysts and parasites looks for intestinal parasites: eggs of roundworms and tapeworms and protozoan cysts such as Giardia. It is performed for persistent diarrhoea, cramps and bloating, particularly after travel or when someone you live with has had parasites. Submit one stool sample, delivered within 2 hours.

Who is this test for

• people with diarrhoea lasting longer than two weeks, particularly after travel,
• people with watery diarrhoea, wind, cramps and greasy, foul-smelling stools typical of giardiasis,
• people with symptoms after drinking untreated water from springs, rivers or lakes,
• people whose household member has a parasitic infection, and children when infection is confirmed in their nursery group,
• people with weakened immunity, in whom Cryptosporidium may cause prolonged and severe diarrhoea,
• people who see worms or tapeworm segments in stools.

What the test reveals

Protozoa, such as Giardia, Cryptosporidium and amoebae, are most often found in stool as cysts or oocysts. Intestinal worms (helminths), such as roundworms and tapeworms, leave eggs, larvae or segments.

Testing includes microscopic stool examination for eggs and cysts, detecting many intestinal parasites. For targeted testing for Giardia, Cryptosporidium and the amoeba Entamoeba histolytica, the cause of amoebic dysentery, there is also the Intestinal parasite panel.

For diarrhoea lasting longer than two weeks, particularly after travel, parasite investigation is also recommended by IDSA guidelines. Giardiasis usually develops 1 to 2 weeks after infection.

If diarrhoea is accompanied by blood in stools, a high temperature, severe abdominal pain or signs of dehydration, see a doctor immediately.

How to collect a stool sample correctly

Submit one stool sample for testing.

1. Prepare a clean screw-top container with a spoon in the lid.
2. Collect stool into a clean, dry receptacle or onto paper. It must not mix with urine or toilet water, as this spoils the sample.
3. Use the spoon to transfer a walnut-sized sample into the container. If you see mucus or blood, include that portion.
4. Close the container securely and label it with your first name, surname and date.
5. Deliver the sample to any branch within 2 hours, because it must be fresh for microscopy.

Some substances interfere with testing, so provide a sample before using them or after the stated interval:

Substance	Interval before sample collection
barium (contrast X-ray imaging of the digestive tract) and bismuth preparations	7 to 10 days
antibiotics	2 to 3 weeks
antacids, liquid paraffin and antidiarrhoeal medicines not absorbed from the intestine	do not provide a sample while taking them

Do not stop a prescribed medicine yourself; agree with your doctor when to provide the sample.

Threadworm: perianal tape test rather than stool

The small threadworm (Enterobius vermicularis) is usually not detected by stool testing. Females leave the intestine at night and lay eggs on the skin around the anus, so eggs are rarely found in stool. The main sign is itching around the anus, worse at night, which causes restless sleep in children.

Threadworm is tested using a perianal tape test. It is collected in the morning before washing or using the toilet: clear adhesive tape is pressed onto the skin around the anus and attached to a microscope slide. Do not wash this area for at least the preceding day, preferably two. One negative tape test does not rule out threadworm, so sampling is often repeated on three consecutive mornings.

What the result can and cannot tell you

A positive report identifies the parasite found. Some amoebae visible under a microscope do not cause disease, so the doctor interprets results alongside symptoms and decides on treatment.

A negative result does not always rule out infection. A parasite may remain undetected:

• if absent from that sample, because parasites are shed intermittently in stool;
• early in infection, before eggs or cysts appear in stool;
• if the sample was not fresh or was collected soon after antibiotics, barium or bismuth;
• with parasites living outside the intestine, such as Toxoplasma or Toxocara. These are detected by serological tests in blood.

If results are negative but symptoms last longer than two weeks, the doctor may repeat testing or investigate another cause, such as inflammatory bowel disease, which may be indicated by faecal calprotectin.

How to arrange testing

Testing is available without a referral or appointment: every branch accepts stool samples (listed on the page Contactpage). Prices for all tests and panels are listed in the service price list.

Parasite testing does not detect viruses or bacteria. For acute diarrhoea, the doctor may also request Viral gastro panel 1 (rotavirus, adenovirus and norovirus) or Viral gastro panel 2, which also includes astrovirus.

Frequently asked questions

Does stool need to be collected for three days?

No. Submit one stool sample, delivered within 2 hours. If results are negative but symptoms persist, the doctor may request repeat testing.

Is there a home test for parasites?

You collect the stool sample at home, while testing is performed in the laboratory. The perianal tape test for threadworm is also collected at home according to laboratory instructions.

Does the whole family need testing?

The doctor decides according to the parasite type. Threadworm and Giardia spread easily between household members, so the doctor often advises examination or treatment for them too.