Stool examination

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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During a stool examination, human feces are analyzed for pathogens and blood. This helps the doctor diagnose gastrointestinal diseases and plan therapy. A stool examination is part of a cancer screening examination from the age of 50. Find out more about the procedure and evaluation of the stool examination here!

What is a stool exam?

The color, mass, hardness and smell of human feces provide information about the condition of the digestive tract. Normally, the excrement consists mainly of water, food residues, bacteria and ablated mucous membrane cells. It gets its color from degraded bile pigments.

If there is visible red blood on the stool, it is probably coming from the middle to lower sections of the intestine, such as hemorrhoids, polyps, or diverticula (protrusions of the intestinal wall). A black, shiny stool (tarry stool) is caused by bleeding in the upper digestive tract (such as the esophagus, stomach): The hemoglobin in the blood is broken down by contact with stomach acid and then turns the stool black.

However, blood in the stool may not be visible to the naked eye if there are small amounts from higher intestinal sections that are mixed in with the feces. This so-called occult blood can come from, for example, polyps, diverticula, foci of inflammation and colon cancer.

When do you have a stool exam?

A stool examination is always necessary if there are unclear complaints in the digestive tract such as abdominal pain, cramps, diarrhea or constipation over a long period of time. Especially if you have digestive problems after a trip abroad, a stool examination can provide information about parasites, bacteria or viruses that you have caught on the way.

A stool analysis (examination for blood in the stool) is recommended for people aged 50 and over as part of the early detection of colorectal cancer.

What do you do during a stool examination?

For the stool test, the patient receives a plastic tube from the doctor with a small spatula attached to the screw cap. He has to take small samples from three different places on the stool and put them into the tube. The sealed tube is then given to the doctor, who sends it to a laboratory for evaluation.

Fecal occult blood test

Testing for invisible (occult) blood in the stool is used to identify colon polyps and tumors that bleed frequently. There are now two ways of doing this:

Immunological stool test (i-FOBT)

In medical diagnostics, the immunological stool test has replaced the hemoccult test that was previously used. Both can detect tiny traces of blood in the stool. While the conventional hemoccult test uses a biochemical color reaction, the immunological stool test uses antibodies.

The advantage of the immunological blood test: It detects polyps or tumors more reliably than the old hemoccult test. And it raises the false alarm less often than the haemoccult test: This is also positive if the person examined has consumed raw meat, black pudding or vegetables containing peroxidase (such as cauliflower and radish).

Such false-positive results can cause great concern for the patient and lead to unnecessary, stressful follow-up examinations. The immunological stool test, on the other hand, does not react to these foods, but only to human blood.

However, both can trigger another type of false positive. Because not only intestinal polyps and tumors bleed: Both test methods also react to bleeding gums, gastric bleeding, bleeding hemorrhoids and menstrual blood with a supposedly positive result.

Hemoccult test (guaiac test)

The old method of detecting occult blood in stool, the hemoccult test, is also called the guaiac test. In this biochemical test, the red blood pigment hemoglobin is detected in the stool sample using a special solution. Unlike the immunological stool test, this test also reacts to animal blood and foods containing peroxidase (see above).

Whether immunological stool test or haemocult test: If the result is positive, the doctor will arrange further examinations and a colonoscopy. In this way, the source of the occult blood (polyps, colon cancer, etc.) can be determined.

M2-PK stool test

The M2-PK stool test is also used for the early detection of colon cancer. However, this test does not detect blood in the stool, but rather the enzyme pyruvate kinase: Elevated levels of this enzyme can indicate colon cancer or colon cancer precursors. For a more detailed clarification, the doctor will then arrange for further examinations and a colonoscopy. Conversely, normal enzyme levels in the stool do not mean that there is no colon cancer present.

Helicobacter stool test

Antibodies against the stomach germ Helicobacter pylori can be detected with a Helicobacter stool test. The test is carried out if there is a suspicion of inflammation of the stomach lining or a duodenal ulcer - diseases that are often caused by the bacterium. If the stool examination is positive, i.e. if there is a Helicobacter infection, this is treated with medication.

What are the risks of a stool examination?

A stool examination does not involve any risks. You do not come into contact with the feces yourself, to take the stool sample you use a spatula and with this you put the stool sample into the sample tube, which is then tightly closed and passed on to the doctor for stool analysis.

What do I have to consider after a stool examination?

After submitting the stool samples, there is nothing else to consider, except that you ask your doctor about the results of the stool test and have any further tests carried out if necessary.

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