New Antibody Test Can Definitively Diagnose Irritable Bowel Syndrome

A new blood test that incorporates two antibodies can diagnose diarrhea-predominant irritable bowel syndrome (D-IBS), according to a study published May 13 in PLOS One. For patients with chronic diarrhea, the test can noninvasively distinguish D-IBS from inflammatory bowel disease (IBD), eliminating the need for costly and invasive exploratory testing.

“Having an early diagnosis means patients can avoid years of invasive tests and visits to specialists,” lead author Mark Pimentel, M.D., from Cedars-Sinai Medical Center in Los Angeles, said in a statement. “With these new blood tests, many patients will now be able to proceed right to therapy for their condition.”

To date, diagnosis of IBS has been based on a “diagnosis of exclusion,” the authors say, which has involved a “great deal of expense and morbidity to patients with IBS.” Imaging, endoscopy, colonoscopy, and blood testing have been utilized to rule out alternative “organic” explanations for diarrheal symptoms. While celiac disease (CD) diagnosis has been “greatly enhanced” using serum tissue transglutaminase antibody, a marker has been lacking for definitive diagnosis of D-IBS.

Commonwealth Laboratories (Salem, Mass.) commercially launched the $199 IBSchek test during Digestive Disease Week 2015 (May 17-19; Washington, D.C.). The enzyme-linked immunosorbant-based assay detects the presence of two antibodies—anti-cytolethal distending toxin B (CdtB) and anti-vinculin. The antibodies are associated with alterations in the intestinal microbiota resulting from acute gastroenteritis, usually caused by a bacterial infection. Previous studies have tied resulting alterations from acute gastroenteritis to D-IBS based on breath testing, culture studies, and deep sequencing of small bowel microbial flora.

In the PLOS One study, researchers assessed circulating anti-CdtB and anti-vinculin antibody levels in patients with D-IBS based on Rome criteria (n=2,375), as well as patients with IBD (n=142), CD (n=121), and healthy controls (n=43). Participants with IBD and CD had histologic confirmation of chronic inflammatory changes in the colon or small intestine.

The researchers found that both anti-CdtB and anti-vinculin titers were significantly higher in D-IBS subjects compared to IBD and healthy controls, as well as patients with celiac disease, Crohn’s disease, ulcerative colitis, and celiac disease. The area-under- the-receiver operating curves were 0.81 and 0.62 for diagnosis of D-IBS versus IBD for anti-CdtB and anti-vinculin, respectively. Specificity was lower for both tests’ ability to differentiate IBS from CD. When optimizing the test (an optical density of 2.80 or more for anti-CdtB and 1.68 or higher for anti-vinculin) led to specificity, sensitivity and likelihood ratio of 91.6 percent, 43.7 percent, and 5.2, respectively for anti-CdtB, and 83.8 percent, 32.6 percent, and 2.0, respectively for anti-vinculin.

“[Anti-CdtB and anti-vinculin] represent the first opportunity to make IBS a diagnosis of inclusion rather than a ‘diagnosis of exclusion,’” write the authors, some of whom have financial ties to Commonwealth, which exclusively licensed patent applications for the blood tests from Cedars-Sinai. “As a biomarker, measurements of anti- vinculin and anti-CdtB antibodies could help to identify D-IBS without excessive investigation and may help to target investigations in those where the test is negative.”

Craig Strasnick, Commonwealth’s chief operating officer, says that quantification of the downstream cost savings associated with use of IBSchek is forthcoming in a publication later this year, but that the per patient savings are “substantial.” Additionally, he tells DTET that data validating IBSchek in IBS patients presenting with constipation or mixed symptoms is also forthcoming this year.

Takeaway: A new test that could definitively diagnose IBS could substantially cut costs associated with expensive and invasive workups traditionally used to rule out other causes of diarrheal symptoms.