Immunological stool test (iFOBT)
Christiane Fux studied journalism and psychology in Hamburg. The experienced medical editor has been writing magazine articles, news and factual texts on all conceivable health topics since 2001. In addition to her work for, Christiane Fux is also active in prose. Her first crime novel was published in 2012, and she also writes, designs and publishes her own crime plays.
More posts by Christiane Fux All content is checked by medical journalists.An immunological stool test can be used to detect blood in stool that cannot be seen with the naked eye (occult blood). The background to this is that colon tumors and precursors to colon cancer bleed more frequently than healthy intestinal mucosa. Read here how an immunological stool test works, how safe the test result is and what you have to pay attention to.
What is the immunological stool test?
A quantitative immunological stool test (also: immunological fecal occult blood test / iFOBT or fecal immunochemical tests / FIT) detects the smallest amounts of human blood in the stool. It is used for the early detection of colon cancer. Because intestinal tumors and their precursors often bleed.
The immunological stool test works with the help of special antibodies that only respond to human blood: They bind to the red pigment hemoglobin in the blood.
This is an advantage over the previously used hemoccult test (guaiac test). This also reacts to eaten animal blood (e.g. steak) and to some plant-based foods such as broccoli.
For whom is the immunological stool test useful?
Men and women between the ages of 50 and 54 can have the test carried out annually as a health insurance benefit. From the age of 55, every two years. You can get it from general practitioners, gynecologists, dermatologists, internists, surgeons and urologists, for example.
Colonoscopy is much more informative
Alternatively, men aged 50 and over and women aged 55 and over can have a colonoscopy, which is much more reliable in diagnosing colon cancer. Another advantage is that precursors and smaller tumors can be removed directly. If the results are normal, you can have another colonoscopy ten years later.
With these signs you should see a doctor
However, if you notice symptoms or noticeable changes in yourself, you should consult a doctor as soon as possible. This includes:
- Blood in the stool
- altered chair
- changed stool frequency
- frequent severe abdominal pain
In this case, early detection of colon cancer may be preferred. This also applies to people who have a high risk of colon cancer due to their illness or whose families have colon cancer often or early on. They too should start regular screening tests earlier. Discuss the individual approach with your doctor.
How is the immunological stool test carried out?
The patient takes the stool sample for the test at home with the help of a special collection set that he received from the doctor. It contains instructions for the immunological stool test, collecting paper for the toilet, a tube with liquid and an integrated spatula, a sealable plastic bag and an envelope.
The sample should be given to the doctor by the next day, who will send it to a laboratory for further examination. The result is then available within a few days. A notification is usually only given if anomalies have arisen. In this case, a colonoscopy is necessary for further clarification.
Women who are having their periods should wait until the bleeding has passed a few days before testing.
How reliable is the immunological stool test?
The immunological stool test can detect colon cancer more reliably than the previously used hemoccult test.
Blood in the stool often has other causes
But even if the test shows blood in the stool, a malignant tumor is rarely the cause. In most cases, the blood will come from other sources - such as colon polyps, hemorrhoids, or inflammation in the bowel. Doctors refer to such a connection as a “false-positive” result.
No clear all-clear
Conversely, the fact that no blood was found does not mean with certainty that there is no colon cancer - because some colon tumors do not bleed or at least do not bleed continuously. Doctors refer to this as a "false negative" test result.
The reliability of the test result can also be influenced by medication. For example, proton pump inhibitors make the immunological stool test less reliable, while anticoagulant drugs ensure fewer false-negative and more false-positive results.
One in a thousand is saved
Statistical projections show that out of every 1000 women and men aged 50 and over who regularly test for blood in their stool for ten years, one woman and one man each are saved from death from colon cancer.
In two of the 1000 women, the stool test misses colon cancer - it is only discovered because of symptoms. In 340 of the 1000 women, an abnormal test result occurs at some point during these ten years, so that a colonoscopy is necessary. Intestinal polyps were discovered in 114 women, some of which are considered to be precancerous. Colonoscopy actually found colon cancer in three of the 340 women.
As with women, of the 1000 men mentioned above, two received a false-negative result in the ten years (the existing colon cancer is not detected in the stool test) and 340 a suspicious test result. The latter leads to a colonoscopy. In 155 men, intestinal polyps were identified as the cause of the blood in the stool and in five men it was actually colon cancer.
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