Stool test: Information for women

Photo of a doctor talking to a patient (PantherMedia / Fabrice Michaudeau)

Fecal occult blood tests (FOBTs) can detect hidden traces of blood that may come from tumors or polyps in the colon. If such traces are found, a colonoscopy is performed to determine whether they're actually caused by a tumor or pre-cancerous tissue changes. It has been proven that, when combined with a colonoscopy, FOBTs can lower the risk of dying of colorectal cancer.

FOBTs detect non-visible (occult) traces of blood in stool samples. "Hidden" blood in stool could be a sign of colorectal polyps or cancer. It is usually caused by something else, though, such as an inflammation of the lining of the stomach (gastritis).

This is why stool blood tests are meant to be used as preliminary tests. If the FOBT results are abnormal, a colonoscopy is done to take a closer look. This is necessary in order to find out what is causing the bleeding. So doing an FOBT makes the most sense if you're also prepared to have a colonoscopy if the test results are abnormal.

In Germany, statutory health insurers will cover the costs of immunological stool tests used for this purpose. They are now used instead of the chemical stool tests because they are more accurate. Women between the ages of 50 and 54 are eligible for one FOBT per year, and then every two years after they turn 55. If the test detects traces of blood, the results of the colonoscopy that is then performed will determine what needs to be done next. After the colonoscopy, people don't need to have another FOBT for a few years.

What does an FOBT involve?

Colorectal cancer screening is voluntary. If you would like to have an FOBT, you have to ask your doctor about it. The test will typically be handed out to you by a doctor who specializes in one of the following areas:

  • General medicine (family doctors or general practitioners)
  • Internal medicine
  • Urology
  • Gynecology

The doctor's practice will be able to answer any questions you have about using the test. The instructions that come with the test should be helpful too. The test is done at home. The test results will only be accurate if the stool sample is tested within five days. The doctor's practice will tell you when it has to be handed in by so that it can be tested in time.

The test package will contain everything necessary for taking the sample. Special paper is put into the toilet to catch the stool. The sample is then removed using a small stick. The sample is placed in a tube that can be sealed so it is airtight. The tube is put in an envelope and dropped off at the doctor's office. They send the sample to a lab for analysis.

Important to know: The doctor's practice will only notify you if blood traces are found. If you don't hear anything, then the test results were normal.

How reliable are FOBTs?

FOBTs are relatively simple to do and have no direct side effects. But they aren't always very reliable. Test results are often abnormal, without cancer being the underlying cause. This is called a "false positive" test result. This is because other problems can result in bleeding too, including stomach ulcers or inflammations in the stomach or bowel.

Also, colorectal cancer and polyps don't always leave traces of blood in stool. Because of this, any one test will fail to detect about 30% of tumors and many polyps. This is known as a “false-negative” test result. So it's important to take any symptoms that concern you seriously – even if your last test results were normal.

What kind of results can you expect if you regularly have an FOBT?

Blood traces are found in the stool of about 50 out of 1,000 women who have FOBTs. These women are then invited to have a colonoscopy. The other women can have the test again every one to two years. The stool test is only helpful if you have it done regularly over the course of many years. But this will increase the chances of having abnormal results. The following illustration shows what results can be expected if 1,000 women regularly have an FOBT for ten years from the age of 50.

Illustration: At a glance: What happens if 1,000 women have the test?At a glance: What happens if 1,000 women have the test?

Can regular FOBTs lower your risk of colorectal cancer?

Several studies have looked into what womencan expect from regularly testing for hidden (occult) blood traces in their stool. The research shows that these stool tests can lower the risk of dying of colorectal cancer. But there is no proof that they can lower the risk of getting bowel cancer. The following tables summarize the main results separately – for women who are 50 years old and for women who are 60 years old. These results apply to a period of ten years, starting at the age given.


Out of 1,000 women who are 50 years old . . .
  . . . will die of colorectal cancer:
 Without screening 1
With the stool test (FOBT) 0 to 1


This means that

out of 1,000 women . . .

. . . death from colorectal cancer

is prevented in

up to 1 more woman.


Out of 1,000 women who are 60 years old . . .
  . . . will die of colorectal cancer:
Without screening 3
With the stool test (FOBT) 2 to 3


This means that

out of 1,000 women . . .

. . . death from colorectal cancer

will be prevented

in 1 more woman. 

Other types of stool tests

Some doctors offer women other types of stool tests for colorectal cancer screening that they would have to pay for themselves (in Germany these are known as "individual health care services," or IGeL for short). These tests include the M2-PK test and a stool DNA test. The M2-PK test looks for an enzyme in the stool that is thought to be a sign of colorectal cancer. The DNA test looks for fragments of genetic material from cancer cells found in stool. But tests for blood in the stool (FOBTs) are the only tests that have so far been shown to lower the risk of dying of colorectal cancer. So you can safely turn down offers of any other types of tests.