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Tests and Diagnosis for IBS

By William Salt, M.D. ; Updated August 14, 2017

IBS can be diagnosed with a careful history of symptoms, family history and simple tests based upon the IBS subtype to consider diseases and conditions that can mimic IBS. Here is a 10-step diagnostic strategy:

1) Getting an Accurate IBS Diagnosis is Important

A secure diagnosis reassures patients about the nature of their symptoms and avoids unneeded testing, procedures and surgeries. Understanding the diagnostic process and that health care professionals often differ in approach can empower patients to be more collaborative in their diagnosis and treatment.

2) Recognize IBS Symptoms and Determine IBS Subtype

Both diagnosis and treatment are determined by which IBS subtype you have.

3) Exclude Troublesome Medications and Supplements

Some medications and supplements can either cause or aggravate IBS symptoms, such as: calcium, magnesium, iron, nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, antidepressants, antiparkinsonian drugs, antipsychotics, calcium-channel blockers, metformin and opioids.

4) Consider Family History

If any first-degree relative (parent, sibling, child) has celiac disease, inflammatory bowel disease or colorectal cancer, more extensive testing may be necessary.

5) Assess for “Red Flags”

Go to the doctor to see if you have IBS if one of the following "red flags" occur: severe or progressively worsening symptoms, unexplained weight loss, diarrhea, vomiting, blood in the stool and unexplained iron-deficiency anemia.

6) Ask About Bacterial Gastroenteritis

Post infectious IBS (IBS-PI) can occur following acute bacterial food poisoning with Campylobacter, Salmonella, Shigella or E. Coli. Many do not recall the event because it was mild and/or do so upon learning about IBS-PI.

7) Consider Associated Small Intestinal Bacterial Overgrowth (SIBO)

Many patients with IBS have associated SIBO with symptoms of IBS-D, IBS-C or IBS-M. Bloating and distention are clues to the presence of SIBO, which may be amenable to specific treatment. Commonwealth Laboratories offers both a new IBSchek blood test for IBS-PI complicated by SIBO as well as a hydrogen breath test for SIBO that patients can conduct themselves. Small intestinal evaluation may be required, since several diseases and disorders interfering with normal peristalsis and flow of intestinal contents can underlie SIBO.

8) Conduct Diagnostic Testing

Extensive and invasive testing are usually not necessary if red flags are absent and basic tests are normal.

All IBS subtypes: A CBC (complete blood count) and age-appropriate colorectal cancer screening is recommended.

IBS-C: If severe and unresponsive to treatment, conduct special testing for slow colon transit (colonic inertia) and obstructed defecation (dysynergic defecation).

IBS-D: Consider fecal incontinence; malabsorption of fat, carbohydrates or bile acids, particularly if symptoms are triggered by meals; inflammatory markers (C-reactive protein and stool calprotectin); celiac disease blood testing (IgA tTG, or tissue transglutaminase and quantitative IgA); IBS-PI; and, if a colonoscopy is performed, biopsies for microscopic colitis.

IBS-M: Consider inflammatory markers (C-reactive protein and stool calprotectin); celiac disease blood testing (IgA tTG, or tissue transglutaminase and quantitative IgA); stool diary and plain abdominal film X-ray to assess for stool accumulation, which is managed as IBS-C; and IBS-PI.

IBS-PI: Perform the IBSchek blood test and consider hydrogen breath testing.

9) Consider Evaluating for Diseases Similar to IBS

“Differential diagnosis” is considering diseases and conditions that have symptoms similar to those of IBS.

These diseases include: celiac disease (blood test); malabsorption disorders (dietary exclusion/elimination and hydrogen breath testing); bile acids (a trial with a bile acid-binding drug); fat in stool (stool pancreatic elastase test; dietary exclusion/elimination); inflammatory bowel disease, or IBD (blood and stool tests); Crohn’s disease; microscopic colitis (biopsies of the colon); hormone imbalances, especially thyroid disease (blood tests); colorectal cancer (blood in the stool); iron deficiency anemia; and chronic GI infections (stool testing).

10) Record the Multi-Dimensional Clinical Profile (MDCP)

The Rome Foundation has developed the MDCP 1st Edition for diagnosis of FGIDs and will soon update to a 2nd edition, including an online decision support system. There are five categories: 1) FGID Diagnosis; 2) Clinical Modifiers — other FGIDs (e.g., IBS subtype) and coexisting symptoms/functional somatic syndromes (e.g., fatigue/fibromyalgia); 3) Impact on Daily Activities — none/mild/moderate/severe; 4) Psychosocial Modifiers — psychological/psychiatric symptoms/syndromes and major stressors (e.g., depression and history of abuse); and 5) Physiological Modifiers of Function and Biomarkers (e.g., abnormal colonic transit study and positive IBSchek).

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