Irritable bowel syndrome (IBS) is a common digestive disorder that affects 10%-15% of Americans and is notoriously difficult to diagnose. Not only are there no definitive biomarkers or tests, but its clinical presentation varies considerably between patients and in each one over time.

In addition, many of the hallmark symptoms of IBS — pain, constipation, diarrhea and bloating — are associated with a host of other gastrointestinal diseases, including some with increased mortality and morbidity, such as colon cancer, Crohn's disease and ulcerative colitis.

The dilemma clinicians face is how much initial testing they should conduct to rule out more serious conditions before moving forward with the diagnosis and treatment of IBS.

"It's a difficult question because, on the one hand, if we gave every person with gastrointestinal symptoms a colonoscopy for fear they had colon cancer, not only would that be massively expensive for the system and the patient, but it could also cause the patients net harm," says Dr. Eamonn Quigley, director of the Underwood Center for Digestive Disorders and chief of Gastroenterology at Houston Methodist. "On the other hand, what about that nagging fear that 'it could be something else?' How do we ensure that we're not missing an opportunity to catch a serious disease in its early stages while it's easier to treat?"

To answer his own question, Dr. Quigley has developed an evidence-based approach that hinges on an enhanced initial consultation, hyper-detailed history and individualized test schedule based on biographical context. His findings, published in Current Opinions in Gastroenterology and presented in a recent American College of Gastroenterology course, offer referring primary care physicians and GI specialists a sensible pathway for the diagnosis and treatment of IBS while maintaining vigilance against less likely, higher risk culprits.

It's all about the history

Clinical features, patient demographics and context can help to significantly narrow the differential diagnosis of the individual whose symptoms suggest IBS and ultimately lead to a positive diagnosis. For this reason, Dr. Quigley recommends allotting significant time for the initial patient interview.

"It may seem obvious, and applicable to every disease, but with irritable bowel syndrome, I cannot overstress the importance of taking the time to sit down with the patient and get a detailed clinical history," says Dr. Quigley. "GI issues are so common and part of everyone's vocabulary, you have to figure out exactly what the patient means by diarrhea, constipation, bloating or pain."

Not only does taking a detailed clinical history give clinicians a more accurate picture of the individual's symptoms, says Dr. Quigley, it allows them to make sure the patient doesn't have blood in the stool, nausea, vomiting, weight loss or anemia, all red flags for more serious conditions.

The next step is combining patient history with demographic and geographic information to calculate individual risk profile.

"IBS is most prevalent in young women aged 20-40 and is by definition chronic," Dr. Quigley says. "If a 25-year-old female patient presents with ongoing stomach pain and constipation, the likelihood of a serious underlying condition is extremely remote. But if the patient is in her 60s when she develops stomach pain and constipation for the first time, that raises a red flag for me that it might be something else."

Process of elimination

The absence of a universally accepted and applicable biomarker for IBS doesn't preclude diagnostic testing. Wherever indicated, widely available serological and fecal tests can bolster the diagnosis by excluding other options.

"We now have information that shows certain basic, noninvasive tests can be very helpful," Dr. Quigley explains. "I typically recommend a full blood count and chemistry panel, including erythrocyte sedimentation rate. I also recommend measuring both the level of calprotectin in the stool and the level of C reactive protein in the blood because together that forms a very sensitive test for detecting inflammatory bowel disease."

Also, if the patient lives in North America or Western Europe, where celiac disease is relatively common, serological screening for the immune disorder may be recommended.

Proceeding to more invasive testing should be dictated by clinical presentation and context.

Although colorectal cancer is the most feared missed diagnosis, studies show that it and other non-IBS diseases are extremely unlikely to occur in patients who don't have at least one of the following red-flag symptoms: nocturnal diarrhea, older age at symptom onset, weight loss, gastrointestinal bleeding, anemia, fever or family history of colon cancer.

Colon cancer screening is recommended for patients over 45 who have never had a colorectal cancer screening before or who have a red-flag symptom.

Tests related to other conditions, including microscopic colitis, idiopathic bile acid diarrhea, small intestinal bacterial overgrowth and disaccharidase deficiency, may be recommended but only if diagnostic indicators are present.

"The inclination to investigate every individual with IBS-type symptoms until all possible alternatives have been excluded can and should be resisted," cautions Dr. Quigley.

Getting the irritable bowel syndrome diagnosis right

Careful attention to detail in the clinical evaluation and recognition of other clinical features, such as anxiety, depression and somatization, can further enhance diagnostic accuracy.

"The good news is, over the decades, I've sensed a real change among patients — that they are much more accepting of the diagnosis of IBS because there's better information out there, better ways to manage and live with the disease, and less chance of a misdiagnosis than ever before," says Dr. Quigley.