How is IBS Diagnosed?

Understanding your IBS subtype is important as most IBS treatments are targeted at normalizing bowel movements as an initial step. IBS subtypes are based on bowel movements on the days a patient is symptomatic and absent of the effect of any medication or supplements to treat diarrhea or constipation.

Bristol Stool Form Scale

The Bristol Stool Form Scale (BSFS) can be a useful tool to use when communicating with your doctor about whether you are experiencing diarrhea or constipation.

The four subtypes (IBS-C, D, M, U)

There are four subtypes of IBS:

1. IBS with constipation, referred to as IBS-C. These patients will primarily have constipation (BSFS type 1 or type 2 stools) on the days they have symptoms.
2. IBS with diarrhea, known as IBS-D. These patients will primarily have diarrhea (BSFS type 6 or type 7 stools) on the days they have symptoms.
3. IBS-M, which is IBS with mixed bowel habits. These patients experience a mixture of diarrhea (BSFS type 6 or type 7 stools) and constipation (BSFS type 1 or type 2 stools).
4. IBS unclassified, also known as IBS-U, where patients will meet the general criteria of IBS but rarely have diarrhea or constipation.

Standard testing and evaluation

The evaluation for IBS should include a careful history and review of symptoms, an in-office physical exam, as well as laboratory testing, including blood tests and stool tests. Guidelines also recommend colon cancer screening starting at age 45 for average-risk individuals in the United States.

Prior to making a diagnosis of IBS, diagnostic testing should include:

• A complete blood count to evaluate for the presence of anemia.
• Blood tests to evaluate for serologic markers of celiac disease as patients with IBS and gastrointestinal symptoms may ultimately be found to have celiac disease. A patient should be consuming gluten at the time of the testing, otherwise the test may result in a false negative result.
• In patients with chronic diarrhea, the provider should also consider testing to evaluate for infections such as Giardia or C Difficile as well as signs of inflammation (a blood test for C-reactive protein, stool calprotectin or stool lactoferrin), which can be seen in inflammatory bowel disease. Depending on the degree and severity of diarrhea, a colonoscopy with biopsies may also be appropriate to evaluate for an inflammatory condition called microscopic colitis.

Red-flag or alarm symptoms

As part of the process, the healthcare provider should also review alarm or red-flag symptoms that suggest an alternate diagnosis to IBS. These include:

• Weight loss
• Blood in the stool
• Black stool, which suggest upper gastrointestinal bleeding
• Diarrhea that frequently disrupts nighttime sleep, also referred to as nocturnal bowel movements
• Sudden new onset of symptoms especially after age 45
• Or a family history of inflammatory bowel disease, celiac disease or gastrointestinal cancers

If any of these symptoms are present, additional testing such as endoscopy, colonoscopy, blood or imaging tests (CT, MRI, or ultrasound) may be considered.

If the above testing is negative and a patient's history and symptoms meet the criteria of IBS, a diagnosis of IBS can be made.

Antibody testing

There is a blood test called IBSchek that measures for 2 antibodies against bacteria elements called cytolethal distending toxin B and vinculin. These antibodies have been shown to be higher in patients with IBS-D compared to healthy individuals, patients with celiac disease and patients with inflammatory bowel disease. While these antibody tests can be helpful to distinguish IBS-D from conditions such as inflammatory bowel disease, on their own they are not sufficient to diagnose IBS. Specifically, the test panel has a lower sensitivity, meaning that a negative result cannot rule out IBS-D. Most experts agree that further evaluation of this test panel is necessary before it is recommended for routine use in clinical practice.

Many conditions can present similarly to IBS. Part of the diagnostic process is to evaluate for these other conditions through a combination of clinical history and diagnostic testing.

These alternate diagnoses include:

• Celiac disease: Celiac disease is an autoimmune condition triggered by gluten exposure in the diet. It can cause bloating, diarrhea, weight loss, and nutrient deficiencies—symptoms that can appear very similar to IBS. Celiac disease is diagnosed by a simple blood test that checks for antibodies against gluten-related proteins, followed by an intestinal biopsy if the blood test is positive. Importantly, testing for celiac disease should be done before removing gluten from the diet, since going gluten-free can result in a false negative result.
• Non-celiac gluten sensitivity: Non-celiac gluten sensitivity can present similarly to celiac disease and IBS-D. However, antibody testing and intestinal biopsy will be normal for these patients. Unlike IBS-D, symptoms of non-celiac gluten sensitivity should resolve or at least significantly improve with elimination of gluten from the diet.
• Bile Acid Malabsorption: Bile acid malabsorption is a condition where bile acids secreted by the liver are not efficiently reabsorbed by the small intestine. As a result, these bile acids can lead to the development of diarrhea and IBS-D like symptoms. Studies have shown that around 25% of patients diagnosed with IBS-D in fact have bile acid diarrhea. Testing for bile acid malabsorption is not readily available in the US, therefore many clinicians will prescribe a trial of medications called bile acid sequestrants to assess for symptom improvement. Commonly, patients who have had their gallbladder surgically removed are at increased risk for bile acid malabsorption.
• Inflammatory bowel disease: Inflammatory bowel disease (IBD) is a group of immune mediated conditions which include Crohn's disease and ulcerative colitis. Unlike IBS, which does not involve structural damage to the intestines, IBD involves visible inflammation on the surface of the intestines alongside other structural changes. Patients may have diarrhea, abdominal pain, blood in the stool, and weight loss. To rule out IBD, testing should include blood tests looking for markers of inflammation, stool tests for inflammatory proteins like calprotectin, and sometimes a colonoscopy with biopsies.
• Colon cancer: While less common, especially in younger patients, colon cancer can present with changes in bowel habits, bloating, abdominal pain, and iron deficiency anemia. For people over age 45, or younger if they have risk factors such as a family history of colon cancer, screening with a colonoscopy is an important step. If someone with IBS-type symptoms also reports what we call "alarm" symptoms like blood in the stool, unexplained weight loss, or anemia, a colonoscopy should be done to exclude cancer.
• Microscopic Colitis: Microscopic colitis is a chronic immune mediated disease of the colon which causes watery, non-bloody diarrhea. Diagnosis requires colonoscopy with biopsies of the colon as the colon typically appears visually normal. There are two subtypes of microscopic colitis, lymphocytic colitis and collagenous colitis, which can be identified on biopsies. Women are three times more likely than men to be affected, and 80% of patients are over age 50. Smoking, medications such as PPIs, NSAIDs, and SSRIs are all known risk factors.
• GI Infections: While most bacterial and viral infections are self-limited and resolve within a few weeks, chronic diarrhea exceeding 4 weeks should be evaluated with testing for C Difficile (bacteria) and Giardia (parasite) through stool testing. Broader testing for other bacteria and parasites can be considered based on the clinical history.
• Endometriosis: Endometriosis is a condition where endometrial lesions are found outside the uterine cavity. As the bowel is a common site for endometrial lesions, symptoms of endometriosis can present very similarly to IBS and should be considered as a possible diagnosis in premenopausal women with IBS symptoms. Symptoms that are suggestive of endometriosis include cyclical exacerbation of IBS-like symptoms with the menstrual cycle, pain with the menstrual cycle, pain with urination, pain with sex, or pelvic pain outside of bowel symptoms. It's important to note that IBS and endometriosis can overlap, and patients with endometriosis have a three-fold increased risk of having IBS.
• Carbohydrate intolerances: Carbohydrate intolerances are conditions where your body struggles to properly digest certain types of sugars or carbohydrates. Common intolerances include lactose and fructose. Breath testing can be done to evaluate for carbohydrate intolerances. Alternatively, a careful history with a dietitian to identify potential intolerances followed by a trial of elimination and rechallenge of potential offenders can be done to evaluate for carbohydrate intolerances.
• Sucrase-isomaltase deficiency: This is a deficiency of the enzyme complex required to digest sucrose (ordinary table sugar) and large starches. The enzyme sucrase-isomaltase is typically located on the surface of the small intestine. While some cases present in infancy, development of IBS-like symptoms later in life have been recognized recently. Estimates suggest that up to 5 to 8% of patients with IBS-like symptoms may have a sucrase-isomaltase deficiency. The diagnosis should be considered in patients who associate symptoms with high sucrose foods (juice, fruit or candy) or starchy foods, or who don't respond to traditional IBS therapies. The deficiency can be diagnosed with duodenal biopsies, breath testing or a trial of treatment with enzyme replacement therapy for sucrose digestion.
• Exocrine pancreatic insufficiency: This is a condition where the pancreas does not produce adequate amounts of digestive enzymes. Risk factors include cystic fibrosis, history of chronic pancreatitis, and prior pancreas surgery. Symptoms can present similarly to IBS-D and include abdominal pain, bloating, cramping and diarrhea. In severe cases, patients can develop weight loss, vitamin deficiency and greasy stools. Exocrine pancreas insufficiency can be diagnosed with stool testing and treated with replacement enzymes.
• Thyroid problems: Abnormal levels of thyroid hormones can result in gastrointestinal symptoms. Most commonly, hypothyroidism (too little thyroid hormone) results in constipation, whereas hyperthyroidism (excess thyroid hormone) can result in diarrhea. Thyroid levels can be checked via blood tests and should be considered as part of the initial evaluation for IBS.

SIBO and IMO

SIBO, or small intestinal bacterial overgrowth, is a condition in which there are excessive numbers or an imbalance of bacteria in the small intestine. Symptoms and features that are often attributed to SIBO frequently overlap with the symptoms that define IBS.

The relationship between SIBO and IBS is complicated, and expert opinions on the relationship between SIBO and IBS vary. Here are some key takeaways:

• SIBO is a condition in which there is an excess or overgrowth of bacteria in the small intestine. This can lead to symptoms similar to IBS-D such as bloating, abdominal pain, diarrhea and gas.
• There is a related condition called Intestinal Methanogen Overgrowth (or IMO) where there is an overgrowth of microbes called archaea in the gut. This most commonly results in constipation and symptoms similar to IBS-C.
• In clinical practice, both SIBO and IMO are typically diagnosed using breath testing, which can detect an increase in gas produced by the bacteria or archaea.
• If a patient tests positive for SIBO or IMO, this can be treated with antibiotics, including an antibiotic called rifaximin, which is also FDA approved to treat IBS-D.
• Some studies have shown that SIBO is more prevalent in patients with IBS, and we do know the microbiome plays an important role in IBS.
• Most experienced clinicians believe SIBO or IMO are secondary diagnoses in that they are caused by other conditions such as a history of anatomic abnormalities, abnormal gastrointestinal motility, celiac disease, or Crohn's disease.

Due to the complicated relationship between SIBO and IBS and varying expert opinions, we discuss SIBO in more detail during our In The Office segments with our experts later in the course.

Hypermobility, Dysautonomia, and Mast Cell Conditions

Some patients with IBS may also have hypermobility, dysautonomia or mast cell conditions. Hypermobile Ehlers-Danlos syndrome or hypermobility spectrum disorder (hEDS/HSD) affects the mobility of joints and connective tissue. Postural orthostatic tachycardia syndrome (POTS) is a condition that affects the autonomic nervous system and regulation of heart rate and blood pressure. Mast cell activation syndrome (MCAS) is a condition in which mast cells release immune mediators inappropriately. These conditions often overlap with each other as well as disorders of gut brain interaction such as IBS.

The relationship between these conditions and IBS is complex, and experts are still learning more about how these conditions overlap and optimal management strategies. Here are some key takeaways:

• Many patients with hEDS/HSD experience gut symptoms and meet criteria for DGBI. Symptoms that overlap with IBS, including bloating, abdominal pain, constipation, or diarrhea, are common.
• GI symptoms from these conditions are thought to come from the same underlying processes seen in IBS, including increased visceral sensitivity, changes in gut motility, and altered nervous system communication. These mechanisms are incompletely understood and remain an area of further investigation.
• Constipation-predominant symptoms (IBS-C) are especially common in people with hypermobility.
• When POTS is present, symptoms like nausea, bloating, and changes in bowel habits can be more pronounced. Treating the underlying POTS may help address GI symptoms.
• When MCAS is suspected, certain foods (high in histamines) or triggers such as heat, physical or emotional stress may lead to activation of mast cells, experienced as flushing, itching, or gut symptoms.
• Any diet changes, such as a low-FODMAP or low-histamine diet, work best with guidance from a dietitian to prevent overly restrictive diets.

Recognizing these overlapping conditions in patients with IBS is important to effectively treat symptoms. Clinical guidance suggests a multi-system approach often involving multiple specialists to effectively manage symptoms. For patients with IBS, this involves combining IBS treatments with treatments aimed at treating these other conditions. Management of these conditions will likely continue to evolve as more research and investigation into the overlap is conducted.

Pelvic floor dysfunction

Pelvic floor dysfunction can be seen among patients with IBS, particularly those with IBS-C or IBS-M. Diagnosis of pelvic floor dysfunction requires specialized testing, which may include a balloon expulsion test, anorectal manometry and defecography.

In a balloon expulsion test, a small balloon filled with water is inserted into the rectum. The patient is then evaluated to see if they are successfully able to push the balloon out and timed during the process. This is intended to simulate a bowel movement and assesses the degree of difficulty a patient experiences evacuating stool.

During an anorectal manometry, a small catheter with sensors is inserted into the rectum. Pressure in the pelvic floor muscles is measured through the sensors when the patient is at rest, followed by certain maneuvers: squeeze, push/bear down and cough. Additionally, a small balloon at the end of the catheter is also gradually inflated while in the rectum to test how well the rectum detects fullness.

Both these tests help evaluate the strength and coordination of the pelvic floor muscles required to successfully evacuate a bowel movement.

Defecography is an additional test that may be performed depending on the result of the balloon expulsion test and anorectal manometry. This is an imaging test where a soft paste (or gel) is gently placed into the rectum, and patients will be asked to squeeze, hold, and then push the paste out, simulating a bowel movement. Radiographic images are taken during this time using either a low-dose X-ray or an MRI scanner.

Dyssynergic defecation is a condition where the pelvic floor muscles fail to coordinate properly during a bowel movement. Symptoms of dyssynergic defecation include:

• excessive straining during a bowel movement
• sensation of incomplete evacuation
• feeling as if stool is stuck during a bowel movement
• needing to use a finger to manually remove stool during a bowel movement
• an insufficient response to medical treatment for constipation

If dyssynergic defecation is diagnosed, guidelines recommend referral to a pelvic floor physical therapist. Biofeedback therapy is a specialized form of pelvic floor physical therapy to retrain the pelvic floor muscles and has been shown to be beneficial in up to 70-80% of patients with dyssynergic defecation.