Test for blood in your stool


Colon cancer is one of the most common cancers in men and women. For women, it is in second place behind breast cancer and in third place for men, behind prostate and lung cancer.

In order to detect the disease early, there is a Germany screening process that consists of various components. An early symptom of the disease is blood in the stool. Most of the time, this blood is not visible to the naked eye, as it is very small. This form of bleeding is also called occult, i.e. hidden. To detect these small amounts, certain tests have been developed in which components of the blood trigger a reaction that leads to a positive test result.

These tests are there

Originally, the blood-in-stool test was performed using a chemical test method. In this test procedure, the presence of blood is checked by means of a color reaction that is triggered by a blood component and a component of the test, the guaiac resin. Various companies offer these tests under names such as Haemoccult or Shirtetect.

In the meantime, however, this test has been replaced by a new method. The new method is based on an immunological reaction. This means that the test is carried out with the help of antibodies that bind to the hemoglobin in the blood. The result of this test cannot be read immediately, but has to be evaluated in a laboratory, but this also enables a more precise determination of the amount of blood. Another accurate test method is the hematoporphyrin test. However, screening is nowadays carried out using the immunological test method as standard.

They are so sure

Since the occult blood test is a screening test, it is important that it has a high sensitivity. Sensitivity means that a high proportion of the test results in sick people are positive. Therefore, one accepts a relatively high number of false positive results. These are test results that are positive even though there is no colon cancer. The original test, which was based on a chemical reaction, had a poor sensitivity of 40%. This means that when the test was carried out once, only 4 out of 10 patients were recognized. However, by repeating the test regularly, 90% of the diseases could still be detected.

The new immunological test has a significantly higher sensitivity and thus recognizes a higher proportion of diseases. It is important that despite positive tests, you do not necessarily have colon cancer. Blood in the stool can also occur from hemorrhoids or a harmless injury. In addition, the old tests reacted with food components and thus showed a false positive result.

For other causes of blood in the stool, see: These could be causes of blood in the stool!

This is how you work

The old test uses a biochemical test procedure. The test consists of a strip of paper to which 2 stool samples from 3 stool movements are applied at home. The test substance on the strip consists of guaiac resin. Hydrogen peroxide is then dripped onto the test strip. If there is blood in the stool, a color reaction from white to blue occurs, in which guaiaconic acid, which is contained in guaiac resin, becomes guaiac blue. The reaction is triggered by an enzymatic activity of the heme contained in red blood cells.

The immunological test, which has replaced the chemical test procedure, is carried out with the help of antibodies. The test is also carried out at home. A stool sample is taken with the help of a spatula, this is placed in a tube and then taken to the doctor, who then sends the stool sample to a laboratory for evaluation. Antibodies are given to the stool sample in the laboratory. These antibodies bind very closely to the hemoglobin contained in the red blood cells. Various technical processes can then be used to determine whether and how much blood was contained in the stool sample.

Who should be tested for blood in stool?

You should have blood in your stool every year from the age of 50 using an immunological test. From the age of 55, an examination every 2 years is sufficient, since from the age of 55 a colonoscopy should be performed every 10 years. This close examination is part of the screening program for the early detection of colon cancer. However, if you are at an increased risk of colon cancer, for example if a close relative developed colon cancer very early, a colonoscopy is performed at a young age.

Also read: Colon Cancer Screening - What You Should Know!

Can I do the test myself?

You can do the occult blood test yourself at home, provided you are able to do so. The test tube for the immunological examination can be obtained from a doctor who is authorized to diagnose cancer early. They will also inform you how to correctly take the sample. You can then take the tube home with you. With the help of the enclosed step-by-step instructions, you can then take the stool sample and send it to the doctor as quickly as possible. This is followed by the laboratory examination. Your doctor will inform you of the results and how to proceed as soon as the laboratory has evaluated the sample. The costs for the examination are covered by the health insurance.

What do I do if the test is positive?

It is very important that a positive result does not constitute a diagnosis. There may be several possible causes for evidence of hidden blood in the stool. It is important, however, that a colonoscopy must be carried out for every positive result. To do this, you will be referred to a gastroenterologist who will carry out the examination. A colonoscopy can very often determine the cause of the blood in the stool. Only a colonoscopy and a sample can be used to determine whether there is colon cancer or a harmless cause of the bleeding.

Further information on the topic of colonoscopy is available at: Colonoscopy