Diagnostics > Blood Tests

IBS Blood Tests and Biomarkers: What Role Do They Play in Diagnosis?

Dr. Sarah Toler, CNM, DNP

Dr. Sarah Toler, CNM, DNP

Unfortunately, there is no quick test to diagnose irritable bowel syndrome (IBS). Many people who live with IBS symptoms endure long periods of uncertainty before receiving an IBS diagnosis. In some cases, it may take years to be diagnosed with IBS.

IBS is a “diagnosis of exclusion.” This means that all other possible causes of the symptoms have to be excluded in order to diagnose IBS. People with IBS symptoms often need to undergo many tests and procedures to rule out other gastrointestinal disorders.

Some blood tests can provide useful information when people have irritable bowel symptoms. Blood work can provide certain clues, but there is no substance found in the blood that is specific for IBS that is a biomarker.

What is a biomarker?

Biomarkers are substances in the body that can be identified in laboratory tests. Biomarkers can indicate a change in the body, a condition, or provide information on normal biological processes or on the course of a disease. One example of a biomarker is human chorionic gonadotropin (hCG), a hormone that can be detected in the blood and urine during pregnancy. It can confirm a pregnancy and to determine the age of a fetus.

Many different substances can serve as biomarkers, like certain genes, modified proteins, or products of metabolism. For example, if a certain amino acid (compounds of proteins) is not processed due to a genetic defect, it accumulates in the blood. This product will remain in the blood as a biomarker and can help with a disease diagnosis. Biomarkers can be found in the blood, urine, bowel movements, or other fluids and body tissues.

Is there an IBS blood test?

There is currently no blood test to diagnose people with IBS. Irritable bowel syndrome is a diagnosis of exclusion. This simply means that all other possible causes for the symptoms of IBS must first be excluded for IBS to be diagnosed.

For IBS patients, however, this usually means a long wait for a diagnosis, including many extensive examinations and appointments. On average, people with IBS symptoms wait around six years for an accurate diagnosis. Diagnosis by blood test would save people years of pain and discomfort.

Researchers are currently working to identify IBS biomarkers. More research is needed to understand the mechanisms behind IBS. Understanding the origins of the syndrome will lead to better treatment for its symptoms.

Are there IBS biomarkers?

There is currently no biomarker in the blood that can be used to definitely diagnose irritable bowel syndrome.

One of the reasons for this is that there are a few different IBS subtypes. While some people with IBS are more likely to experience constipation (IBS-C), others mainly experience diarrhea (IBS-D). Researchers suspect that there are various mechanisms behind each subtype, which would also lead to different biomarkers.

CdtB antibodies as IBS biomarkers

The CdtB antibody is an antibody against Cytolethal distending toxin subunit B. This bacterial poison, or genotoxin, is produced by Campylobacter jejuni, among others, bacteria which can cause a gastrointestinal infection, or gastroenteritis.

It is believed that IBS may occur as a result of a gastrointestinal infection. During an infection, bacteria form poisons, also called toxins. The immune system then produces 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.

This process is called an autoimmune reaction. These antibodies have been detected in people with IBS who experience diarrhea. While half of people with diarrhea-specific IBS will have this biomarker in their blood, about half do not have an anti-CdtB marker in their blood. In addition, the test does not clearly differentiate between IBS and celiac disease, a condition characterized by an immune reaction to gluten.

Biomarker combinations for IBS

It’s also possible to look at a collection of different biomarkers at the same time. These biomarker panels might give clues about the likelihood of IBS.

The markers in the panel are a collection of indicators of IBS, including inflammation markers, pain mediators, signs of microbial colonization, and breakdown products from serotonin metabolism. Specifically, a panel for IBS might include interleukins (IL-6, IL-8), C-reactive protein (CRP), or the tumor necrosis factor alpha (TNF-α). Taken alone, these markers are very unspecific, but together they may be more representative of the group of symptoms that is indicative of 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 (IBD). The presence of calprotectin in stool makes the presence of IBS less likely, ruling out IBS as a diagnosis.

Another biomarker for IBS is called the lactulose breath test. During this test, a person ingests lactulose, a sugar that is processed into fatty acids, hydrogen, and methane by bacteria in the intestine. An increase in exhaled methane might indicate a certain subtype of irritable bowel syndrome which is characterized by constipation, IBS-C.

The future of biomarkers and IBS

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. More research is needed to identify biomarkers for IBS and simplify the diagnostic process for people living with symptoms of IBS.

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Dr. Sarah Toler, CNM, DNP

Dr. Sarah Toler, CNM, DNP

Sarah Toler is a Certified Nurse Midwife, Doctor of Nursing Practice, and science writer. She focuses on improving women's health and access to health care by working with digital health platforms. Her area of expertise is mental health, particularly the physical manifestations of stress and anxiety.

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