Answers
Which stool tests are done for stomach problems, and what do they show?
Short answer
Stool tests are simple, painless tests that help find infections, hidden bleeding, inflammation in the bowel and problems with digestion. Different tests answer different questions, so your doctor chooses the right ones based on your symptoms.
Common stool tests
- Routine and microscopy: looks for pus cells, blood, parasites and their eggs, and undigested fat
- Stool culture and pathogen tests: look for bacteria that cause infectious diarrhoea
- Occult blood test (FIT): finds hidden blood, used to screen for bowel cancer and polyps
- Calprotectin: shows inflammation in the bowel, helping tell IBS apart from inflammatory bowel disease
- H. pylori stool antigen: checks for H. pylori infection of the stomach, and confirms it has cleared after treatment
- Elastase: checks whether the pancreas is making enough digestive enzymes
How to collect a sample
Use the clean container from the lab. Pass stool onto a clean, dry surface such as a plastic sheet over the toilet, not into water, and take a small amount with the spoon in the lid. Do not mix with urine. Take it to the lab within a few hours, or as instructed.
Before the test
Some medicines affect results. For the H. pylori test, acidity tablets and antibiotics are usually stopped for 2 to 4 weeks beforehand, as advised by your doctor. Tell the lab about recent antibiotics.
What results mean
A positive occult blood test needs a colonoscopy to find the cause; it does not mean cancer. A high calprotectin usually leads to a colonoscopy. A normal stool test does not rule out every problem, so persistent symptoms still need review.
Food and medicines before stool tests
Before the test
- Eat your usual diet; most stool tests need no special diet
- Collect the sample in the lab container, without water or urine
- Hand it in within a few hours, or as the lab instructs
Avoid
- Regular painkillers for joint or body pain before a calprotectin test, if your doctor agrees; they can raise the result
- Acidity tablets and antibiotics before an H. pylori stool test, as advised
- Collecting during your period for occult blood tests
Good to know
- The modern FIT test for hidden blood is not affected by food such as meat or vegetables.
- Tell the lab about any recent antibiotics.
Common questions
How many samples are needed?
Usually one, but some tests, such as looking for parasites, may need two or three samples on different days.
Does a positive occult blood test mean cancer?
No. Most positive results are due to piles, polyps or inflammation. A colonoscopy finds the cause.
Why do I need a stool test for acidity?
The H. pylori stool test checks for an infection that causes ulcers and acidity, and confirms it has gone after treatment.