Antibody tests can aid in IBS diagnosis
DEAR DOCTOR: How accurate is the blood test for irritable bowel syndrome? My gastroenterologist says that one exists but that he doesn’t feel it has been proved effective.
DEAR READER:
Irritable bowel syndrome (IBS) is a disorder characterized by abdominal pain in association with altered bowel movements. Sufferers can have diarrhea or constipation, or they can alternate between the two. IBS affects about 11 percent of the population and accounts for anywhere from 25 to 50 percent of all visits to gastroenterologists. It affects women more than men, with 14 percent of women affected and 9 percent of men. IBS is what’s called a “functional bowel disorder,” meaning that it’s not related to inflammation but to how the bowels contract and relax.
To diagnose IBS, a doctor must rule out other causes for a patient’s symptoms. But newer blood tests can help. One assesses levels of an antibody to the cell membrane protein vinculin; and the other assesses levels of an antibody to a toxin produced by the gut (antiCdtB).
A 2015 study showed that these are not very sensitive tests for detecting IBS. Still, a positive test can point doctors in the right direction. If someone does test positive for the high antibody levels, they likely have diarrhea-associated IBS.
A 2017 study additionally evaluated the antibody levels in people with constipation-associated IBS and people with IBS that fluctuated between constipation and diarrhea. The authors concluded that the results of antibody-level testing in people with constipation-associated IBS was not much different than it was for healthy people.
It’s still important to rule out other potential causes for IBS symptoms of abdominal bloating and altered bowel movements. This can be done with blood tests for C-reactive protein and celiac-disease antibodies; a stool test assessing potential bacterial causes; or a stool calprotectin test, which is positive in inflammatory bowel disease. Most chemotherapy treatments are also given via the cerebrospinal fluid by way of a lumbar puncture.