Do I have IBS? A Short Guide to Diagnostic Testing Challenges

IBS: A Clinical Chameleon - Irritable bowel syndrome (IBS) is a chronic disorder characterized by recurrent abdominal pain and altered bowel habits in the absence of detectable organic disease. What that means is we can’t (yet) take a picture of IBS, run a single blood test for IBS, or do an X-ray for IBS; but it’s still real. Although IBS is extremely prevalent, affecting up to 10% of the general adult population, diagnosing IBS is not always straightforward. Properly diagnosing IBS can be challenging and uncertain for several reasons, including: (1) there is currently no consistent biological marker of IBS, leaving clinicians to rely on patient symptoms alone to make the diagnosis; (2) the symptoms of IBS are often difficult to objectively quantify; and (3) many other conditions can masquerade as IBS. The last fact is most troubling to clinicians and patients, many of whom remain unsettled by the prospect of overlooking alternative diagnoses such as inflammatory bowel disease, microscopic colitis, infectious colitis, small intestinal bacterial overgrowth, celiac sprue, or bile acid diarrhea, among many others. This uncertainty often prompts a series of diagnostic tests to exclude alternative conditions. In other words, many clinicians approach IBS as a diagnosis of exclusion, largely because IBS is a sort of “clinical chameleon.”

Guidelines State that IBS is Not a Diagnosis of Exclusion - Despite the tendency to order diagnostic tests in the face of IBS symptoms, clinical guidelines encourage doctors to make a positive diagnosis on the basis of symptoms alone, and emphasize that IBS is not meant to be a "diagnosis of exclusion." This recommendation is based on extensive evidence, summarized elsewhere, that diagnostic testing is generally low yield in patients fulfilling the Rome criteria who otherwise lack alarming signs or symptoms.One study found that 98% of patients with IBS symptoms end up having IBS, and do not have an another underlying condition after undergoing standard evaluations. However, a more recent study calls this into question, and found that many more people with IBS symptoms end up having something else under the surface. A new study, published by MyGiHealth’s own Dr. William Chey in the March, 2015 edition of the American Journal of Gastroenterology, found that checking a stool test called fecal calprotetin can help distinguish IBS from inflammatory bowel diseases like Crohn’s disease and ulcerative colitis. So, some doctors are reluctant to just diagnose IBS without first checking a few key tests.

Evidence of Poor Guideline Buy-In - The previous Rome guidelines stated that IBS can be diagnosed so long as “there are no structural or biochemical abnormalities,” while the most current guidelines say that IBS can be diagnosed in the absence of “alarm features,” and is “often properly diagnosed without testing.” But these clinical asterisks are understandably difficult for many clinicians to reconcile, and some argue that they raise more questions than they answer. Questions like: What diagnostic tests, if any, should be performed before clinicians can reliably diagnose IBS? Is it really possible to make the diagnosis without any information from diagnostic testing? Or should basic blood tests, at the very least, be drawn in all potential IBS patients? What about testing for celiac sprue, or bacterial overgrowth? And so forth.

Diagnostic testing remains rampant in IBS despite the dissemination of the Rome guidelines. For example, community-based surveys reveal that up to 50% of IBS patients receive a colonoscopy in the course of diagnostic evaluation. Moreover, data indicate that 25% of all colonoscopies performed in the United States are for IBS-type symptoms, and 10% of colonoscopies in patients under 50 years of age are conducted in evaluation of IBS symptoms. Perhaps even more surprising, IBS patients are more likely to undergo abdominal surgeries like removing their gallbladder, appendix, or uterus compared to controls without IBS, despite knowledge that IBS symptoms almost invariably persist following surgery. The high rate of excess abdominal operations in IBS suggests that some surgeries may serve as “diagnostic tests” to evaluate symptom response after removing potential culprit organs – the ultimate exclusionary maneuver in IBS.

To better understand current diagnostic decision making in IBS, we performed a national survey to measure provider beliefs about whether IBS is a diagnosis of exclusion, and sought to measure beliefs about the appropriateness of commonly available diagnostic tests in IBS. We then compared beliefs between a group of 45 recognized experts in IBS and a group of randomly selected community providers. We found that only 8% of IBS experts agreed that IBS is a diagnosis of exclusion, whereas 72% of community providers shared this belief. We found that providers who believe IBS is a diagnosis of exclusion ordered 1.6 more tests and consumed $364 more in diagnostic testing per patient vignette than those who did not (p<0.0001). We also found that experts only rated celiac sprue screening and a complete blood count (CBC) as generally appropriate first-line routine tests in IBS. In contrast, community providers were more likely to order a whole range of tests, including testing the blood and stool for infections, inflammation, and the like. Yet even the experts had extreme variation in their opinion about the appropriateness of many tests — they didn’t all agree. The experts were even varied in their opinion of colonoscopy. In short, experts were more likely than non-experts to comply with published guidelines, but both groups demonstrated variations from guidelines and internal inconsistencies in their beliefs about diagnostic testing.

Why the Disconnect? Why do providers continue to order tests in IBS, despite data that these tests are generally (but not always) low yield? In light of the medical-legal interface in the United States, one possibility is that some clinicians believe that diagnostic testing is a form of inoculation against litigation. But clearly this is a sub-optimal reason to pursue diagnostic testing for any reason, and data from our group and others indicate that the quality of the physician-patient relationship is a critical predictor of outcomes, and likely a more important predictor of litigation than testing proclivity. A second possibility is the belief that even negative diagnostic tests are useful, because they can allay patient concerns about serious illness and provide reassurance. Yet we have shown that a negative colonoscopy, in particular, is not associated with reassurance or improved quality of life in young IBS patients. In fact, we found a trend towards less reassurance in patients receiving a negative colonoscopy (versus no colonoscopy at all). But perhaps the most common reason for diagnostic testing in IBS is that the Rome criteria have a 98% – not 100% – hit rate for IBS. And recent data show it’s lower than that. So no matter how strong the evidence that diagnostic testing is low yield, there is always the real (albeit small) possibility of another underlying condition. This is simply not debatable, particularly in light of evolving data that IBS patients are a heterogeneous population with a core of “pure IBS” surrounded by small sub-sets of alternative diagnoses such as celiac sprue, bacterial overgrowth, bile acid diarrhea, and other masqueraders.

Yet despite this reality, patients and clinicians should keep in mind that time is on their side in IBS. In the absence of alarming features, the IBS masqueraders are typically chronic conditions with slowly evolving natural histories. Moreover, cancer is no more common in IBS patient than controls, and patients over 50 years of age should receive colorectal cancer screening regardless of IBS symptoms. Ultimately, patients and clinicians should use their judgment, and must reserve the right to investigate further if IBS doesn’t “follow the script,” either because of a poor response to therapy, worsening symptoms over time, or development of incident alarming features like weight loss, rectal bleeding, or anemia. Like most things in medicine, diagnostic testing in IBS remains a balance of art and science.