Stool analysis: how to read your parasite and occult blood report

What does a stool test actually look for?

A stool analysis, also called a stool examination or faecal test, is a laboratory investigation that examines a small sample of your stool to detect a wide range of problems. It is not a single test but several examinations performed on the same sample, and each one reveals a different type of information. Your doctor requests the ones that fit your specific symptoms and concern.

The main investigations within a stool test are: ova and parasite examination, which uses a microscope to look for parasites such as amoeba, giardia, and the eggs of intestinal worms; the occult blood test, which detects invisible bleeding; stool culture, which grows the sample to identify disease-causing bacteria such as Salmonella and Shigella; and a check for white blood cells in the stool to distinguish between invasive and non-invasive gut infections.

A stool result alone does not always complete a diagnosis. Your doctor reads it alongside your symptoms, how long they have lasted, your diet and travel history, and any accompanying blood tests. The report provides the data. The doctor builds the diagnosis and the treatment plan from everything together.

How to collect a stool sample correctly

The way you collect the sample directly affects the accuracy of the result. Stool must be collected into a sterile container provided by the laboratory, not any container from home. The amount required is small, usually no more than a teaspoon or whatever the laboratory instructions specify.

The sample must be completely free of urine, because urine kills or distorts parasites and makes the white blood cell count unreliable. Avoid collecting directly from a toilet bowl filled with water, because water can also damage sensitive parasites. The best approach is to defecate into a clean, dry container and then transfer the sample from there.

Speed of delivery to the laboratory matters for parasite testing in particular, because some parasites break down at room temperature within hours and may not be seen under the microscope if the sample is delayed. Well-equipped laboratories provide a preservative solution that is added to the sample immediately after collection to stabilise any parasites. Ask the laboratory in advance for full instructions before the day of the test.

Amoeba and giardia: the most common parasites in the region

Amoebiasis is caused by the parasite Entamoeba histolytica. It spreads through food or water contaminated with the faeces of an infected person. A 2022 study published in the Archives of Razi Institute documented amoeba in stool samples from children with diarrhoea in Mosul, Iraq, reflecting the continued prevalence of this infection across the region. In areas with inadequate sanitation or unreliable water treatment, contamination of water and food is the main route of spread.

Giardiasis is caused by Giardia lamblia, one of the most common intestinal parasites worldwide. It spreads the same way as amoeba, through contaminated water or unwashed hands. A systematic review published in Clinical Infectious Diseases in 2012 linked giardia to chronic diarrhoea in children in developing countries and identified it as a leading cause of unexplained persistent loose stools. Its characteristic presentation is greasy, foul-smelling stools with bloating, abdominal cramps, and fatigue from malabsorption.

An important difference between the two: amoeba can cause amoebic dysentery with bloody mucous stools and severe cramps, and it can rarely spread to the liver causing an abscess. Giardia rarely causes blood in the stool but frequently causes malabsorption and chronic fatigue. Microscopic examination of a stool sample identifies both by detecting their cysts or trophozoites in the specimen.

Worm eggs and other parasites the test can find

The ova and parasite examination looks for a wide range of organisms beyond just amoeba and giardia. These include the eggs of roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura), hookworms, and Strongyloides, among others. These intestinal worms are common in environments with poor sanitation or contaminated soil, and their eggs enter the body through contaminated food, water, or bare feet in the case of hookworms.

Pinworms (Enterobius vermicularis) cause intense anal itching especially at night and are very common in children, but their eggs are not reliably found in a routine stool sample. The specific test for pinworms is the tape test, in which a piece of clear adhesive tape is pressed around the anal opening first thing in the morning before washing, then examined under a microscope to catch the eggs that the female deposits at night.

If your parasite test is negative but your symptoms strongly suggest a parasite, such as chronic diarrhoea, persistent bloating, significant weight loss, or unexplained itching, do not rely on a single negative result. Parasites shed eggs intermittently and not at every bowel movement, which is why doctors recommend collecting three samples on separate days before concluding that parasites are absent.

Occult blood in stool: what it means and how it is interpreted

Occult blood in stool is blood present in quantities too small to change the stool colour or be seen by the naked eye, but detectable by a chemical test. Visibly black or dark red stools are a different and more urgent sign that requires emergency assessment rather than a routine occult blood test. The chemical test is used when bleeding is suspected but invisible.

A positive occult blood result means there is bleeding somewhere along the digestive tract from mouth to anus. The possible causes are wide-ranging: peptic ulcer in the stomach or duodenum, haemorrhoids, anal fissures, benign polyps, and less commonly colorectal cancer. A systematic review and meta-analysis published in the American Journal of Gastroenterology in 2020 confirmed that a positive occult blood test always warrants further investigation to identify the source of bleeding and rule out serious pathology.

There are two types of occult blood test: the older chemical guaiac test (gFOBT), which is affected by eating red meat or raw vegetables before the test and may give a falsely positive result, and the newer immunochemical test (FIT or iFOBT), which is not affected by diet and is more specific for blood from the colon. Most laboratories now use the immunochemical test, but always ask your doctor which type was performed when you receive your result.

What do other findings in the stool report mean?

White blood cells (leukocytes) found in a stool sample indicate intestinal inflammation. Doctors use this finding to distinguish between two types of diarrhoea: invasive infection, in which the organism penetrates the gut wall as with Shigella and amoeba, and secretory infection, in which it does not as with viral gastroenteritis and food poisoning from preformed toxins. This distinction matters because invasive infections typically require antibiotic treatment while most secretory infections resolve with fluid replacement alone.

A stool culture involves incubating the sample in a laboratory medium to identify any disease-causing bacteria present. Results usually take two to three days. It is typically requested for severe diarrhoea, bloody diarrhoea, prolonged diarrhoea, or suspected food poisoning affecting multiple people. If bacteria are identified, a sensitivity test shows which antibiotics will be effective, which is essential given the high antibiotic resistance rates increasingly documented in the Arab world.

The report may also comment on the consistency and colour of the stool, and whether excess fat is present (steatorrhoea), which points to malabsorption. In young children, stool pH may be reported to help distinguish between different causes of diarrhoea. All of these additional details help the doctor build a more complete picture of what is happening in your digestive system.

When does a stool result need urgent medical attention?

Most stool results need routine follow-up with your doctor to discuss the next step. But certain results and accompanying symptoms need faster assessment. A positive occult blood result alongside abdominal pain, unexplained weight loss, or a change in bowel habit deserves prompt evaluation because these findings together may indicate a condition requiring endoscopy.

Visibly black tarry stools or bright red blood not explained by known haemorrhoids is visible bleeding that warrants going to emergency rather than waiting for the next day's test. Severe diarrhoea accompanied by high fever, blood, and a deteriorating general condition is an emergency, not a routine outpatient matter.

If your result comes back negative but symptoms persist for more than two weeks or are getting worse, go back to your doctor. One negative result does not rule out parasites or any other cause of your symptoms. Your symptoms are the true guide alongside the test, not the test alone.

Prevention: how to protect yourself from intestinal parasites

Washing hands with soap and water for at least twenty seconds after using the toilet and before eating is the simplest and most effective step against intestinal parasites. Parasites like giardia and amoeba spread through hands contaminated with infected human faeces, and it takes a very small amount to cause infection.

Bottled, boiled, or properly filtered water is the safest choice in areas where the water supply is unreliable. Some parasites including giardia are resistant to chlorine at the concentrations used in most municipal water systems, so boiling or filtration is more important than relying on chlorine alone. Fruit and vegetables eaten raw should be washed thoroughly with clean water or soaked briefly in a food-safe solution.

In settings of high population density or shared toilet facilities such as schools, camps, and displacement shelters, transmission is easier. The level of hygiene in food preparation and the safety of the water source are the two central pillars of prevention at the household and community level. A child treated for a parasite in a household where others are also infected but untested is likely to be reinfected quickly, which is why doctors sometimes treat all household members together.

Sources

• Dhubyan Mohammed Zaki Z: Prevalence of Entamoeba histolytica and Giardia Lamblia Associated with Diarrhea in Children referring to lbn Al-Atheer Hospital in Mosul, Iraq, Archives of Razi Institute, 2022
• Faqe Mahmood SA, Mustafa HB: Molecular Identification and Prevalence of Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii in Erbil City, Northern Iraq, Polish journal of microbiology, 2020
• Leung AKC, Leung AAM, Wong AHC et al: Giardiasis: An Overview, Recent patents on inflammation & allergy drug discovery, 2019
• Muhsen K, Levine MM: A systematic review and meta-analysis of the association between Giardia lamblia and endemic pediatric diarrhea in developing countries, Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 2012
• Lee MW, Pourmorady JS, Laine L et al: Use of Fecal Occult Blood Testing as a Diagnostic Tool for Clinical Indications: A Systematic Review and Meta-Analysis, The American journal of gastroenterology, 2020
• Rockey DC: Occult gastrointestinal bleeding, The New England journal of medicine, 1999
• Kareem Kadhim D, Abdulsalam Hraija B, Aqeele G et al: Molecular-Genotyping Detection of Entamoeba histolytica in Diarrheic Patients, Archives of Razi Institute, 2023