Medical guidelines on irritable bowel syndrome also discuss which blood values can provide useful information. To date, no substance has been found that is specific for IBS and could therefore act as a so-called biomarker, but there is a lot of research being done in this area.
What is a biomarker?
Biomarkers are substances in the body that can be identified in a laboratory test and can provide information about a change in the body, an illness or its course. One example is human chorionic gonadotropin (HCG), which can be detected in the blood and urine during pregnancy. It enables doctors to determine whether you are pregnant and how far advanced you are.
In principle, many different substances can serve as biomarkers, such as certain genes and modified proteins or metabolic products. For example, if a certain amino acid is not processed due to a genetic defect, it accumulates in the blood. This can help with the diagnosis.
Where can biomarkers be found?
Biomarkers can be found in the blood, urine, bowel movements or other body fluids. In addition to such biomarkers, there are also other diagnostic instruments that can provide the treating doctor with information about the presence of a certain disease. One example of this is the results of depression questionnaires, which can also be used in the diagnosis of IBS.
Is a blood test enough for a diagnosis?
A distinction is often made between specific and non-specific biomarkers. A specific biomarker, if detected, would help diagnose a particular disease. For example, if the thyroid was removed because of a tumor, the detection of certain biomarkers after the operation speaks with a high probability of a recurrence of the cancer.
Most biomarkers, however, are rather unspecific. This means that they provide an indication of a certain process in the body, but their presence does not mean that there is a specific illness. Inflammation markers are an example of this. If they are elevated, you know there's inflammation somewhere in the body, but you cannot yet determine the exact cause. In relation to the diagnosis of IBS, this means that with increased inflammation values, IBS could be the reason, but other diseases could also be the reason for the increase in inflammation markers.
Since many biomarkers are rather unspecific, laboratory examinations must always be interpreted together with the medical history, the symptoms and further examinations.
Why is a biomarker needed for IBS?
IBS is understood as an exclusion diagnosis, so that all other causes for the symptoms of those affected must first be excluded. For IBS patients, however, this usually means a long wait for a diagnosis and many complex examinations. On average, those affected wait around six years for the final diagnosis. It would therefore be desirable to be able to diagnose IBS using a blood test. That is why research is concerned with whether there are specific IBS biomarkers.
Research is also currently underway into the development and mechanisms of IBS, since the cause of the disease has not yet been clearly established. If the origin of a disease is known, therapeutic approaches could possibly be developed.
Are there biomarkers in the blood for IBS?
So far, there is no biomarker in the blood that could be used to clearly diagnose irritable bowel syndrome. One of the reasons for this is that there are many different subgroups of the disease. While some sufferers are more likely to suffer from constipation, others mainly struggle with diarrhea. Doctors suspect that there are various mechanisms behind this, which would also lead to different biomarkers. However, there are some promising substances that may be considered as biomarkers.
CdtB antibodies as IBS biomarkers
One of these promising substances is the so-called CdtB antibody. It is an antibody against “Cytolethal distending toxin B”. This bacterial poison is produced by campylobacter jejuni, among others, which is a bacterial trigger of gastrointestinal inflammation (gastroenteritis).
The theory has long existed that IBS arises as a result of a gastrointestinal infection. During such an infection, the triggering bacteria form poisons. The immune system can then produce antibodies against the bacterial toxins. It is believed that in patients with IBS, these antibodies not only bind the bacterial toxins, but also attack the body's own tissue. Such a process is called an autoimmune reaction. Such antibodies have been increasingly detected, especially in IBS patients who suffer from diarrhea (IBS-D). Nevertheless, this does not seem to be the final breakthrough because around half of those affected do not have an anti-CdtB marker in their blood. In addition, the test could not differentiate between IBS and celiac disease (gluten intolerance).
Biomarker combinations for IBS
Other research groups are trying not to rely on a single biomarker alone. Instead, they record a collection of different biomarkers at the same time (so-called panels). From this, the researchers want to calculate how likely it is that IBS is present. The markers result from the different theories behind the development of IBS: Inflammation markers, pain mediators, signs of microbial colonization and degradation products from the serotonin metabolism are just a few of the factors whose interaction should enable the diagnosis to be made. These include inflammation markers such as interleukins (IL-6, IL-8), C-reactive protein (CRP) or the tumor necrosis factor alpha (TNF-α). Taken alone, these markers are very unspecific. The hope is that the combination will allow clearer statements about the clinical presentation.
Interestingly, the diagnostic capabilities of the biomarker combinations are better if other test results are also considered. In a 2014 study, researchers added test results from a questionnaire to diagnose depression. The test was then able to differentiate better between healthy volunteers and patients with IBS.
Are there alternative biomarkers for IBS?
Blood is not the only substance in which biomarkers can be measured. For example, the detection of calprotectin from stool samples can already suggest the presence of a chronic inflammatory bowel disease. Conversely, it follows that the presence of calprotectin in stool makes the presence of IBS less likely.
There are also indications that molecules in the exhaled air can also indicate whether IBS is present or not. To measure these molecules, patients are given lactulose. This is a sugar that is then processed into methane by bacteria in the intestine. If the amount of exhaled methane increases unexpectedly, this is an indication of a certain sub-form of irritable bowel syndrome, which is characterized by constipation.
The use of biomarkers in the diagnosis of irritable bowel syndrome may sound promising, but so far no biomarker has been established in routine diagnostics. However, research is being done worldwide on such biomarkers and one can look forward to future developments.
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