There’s no test to definitively diagnose IBS. Your health care provider is likely to start with a complete medical history, physical exam and tests to rule out other conditions, such as celiac disease and inflammatory bowel disease (IBD).
After other conditions have been ruled out, your provider is likely to use one of these sets of diagnostic criteria for IBS:
- Rome criteria. These criteria include belly pain and discomfort averaging at least one day a week in the last three months. This must also occur with at least two of the following: Pain and discomfort related to defecation, a change in the frequency of defecation, or a change in stool consistency.
- Type of IBS. For the purpose of treatment, IBS can be divided into four types, based on your symptoms: constipation-predominant, diarrhea-predominant, mixed or unclassified.
Your provider will also likely assess whether you have other symptoms that might suggest another, more serious, condition. These include:
- Onset of symptoms after age 50
- Weight loss
- Rectal bleeding
- Nausea or recurrent vomiting
- Belly pain, especially if it’s not related to a bowel movement, or occurs at night
- Diarrhea that is ongoing or awakens you from sleep
- Anemia related to low iron
If you have these symptoms, or if an initial treatment for IBS doesn’t work, you’ll likely need additional tests.
Your provider may recommend several tests, including stool studies to check for infection. Stool studies also can check to see if your intestine has trouble taking in nutrients. This is a disorder known as malabsorption. Additional tests may be recommended to rule out other causes of your symptoms.
Diagnostic procedures can include:
- Colonoscopy. Your provider uses a small, flexible tube to examine the entire length of the colon.
- CT scan. This test produces images of your abdomen and pelvis that might rule out other causes of your symptoms, especially if you have belly pain.
- Upper endoscopy. A long, flexible tube is inserted down your throat and into the esophagus, which is the tube connecting your mouth and stomach. A camera on the end of the tube allows your provider to view your upper digestive tract. During an endoscopy, a tissue sample (biopsy) may be collected. A sample of fluid may be collected to look for overgrowth of bacteria. An endoscopy may be recommended if celiac disease is suspected.
Laboratory tests can include:
- Lactose intolerance tests. Lactase is an enzyme you need to digest the sugar found in dairy products. If you don’t produce lactase, you may have problems similar to those caused by IBS, including belly pain, gas and diarrhea. Your provider may order a breath test or ask you to remove milk and milk products from your diet for several weeks.
- Breath test for bacterial overgrowth. A breath test also can determine if you have bacterial overgrowth in your small intestine. Bacterial overgrowth is more common among people who have had bowel surgery or who have diabetes or some other disease that slows down digestion.
- Stool tests. Your stool might be examined for bacteria, parasites or the presence of bile acid. Bile acid is a digestive liquid produced in your liver.
Treatment of IBS focuses on relieving symptoms so that you can live as symptom-free as possible.
Mild symptoms can often be controlled by managing stress and by making changes in your diet and lifestyle. Try to:
- Avoid foods that trigger your symptoms
- Eat high-fiber foods
- Drink plenty of fluids
- Exercise regularly
- Get enough sleep
Your provider might suggest that you eliminate from your diet:
- High-gas foods. If you experience bloating or gas, you might avoid items such as carbonated and alcoholic beverages and certain foods that may lead to increased gas.
- Gluten. Research shows that some people with IBS report improvement in diarrhea symptoms if they stop eating gluten (wheat, barley and rye) even if they don’t have celiac disease.
- FODMAPs. Some people are sensitive to certain carbohydrates such as fructose, fructans, lactose and others, known as FODMAPs — fermentable oligosaccharides, disaccharides, monosaccharides and polyols. FODMAPs are found in certain grains, vegetables, fruits and dairy products.
A dietitian can help you with these diet changes.
If your problems are moderate or severe, your provider might suggest counseling — especially if you have depression or if stress tends to make your symptoms worse.
Based on your symptoms, medications may be recommended, including:
- Fiber supplements. Taking a supplement such as psyllium (Metamucil) with fluids may help control constipation.
- Laxatives. If fiber doesn’t help constipation, your provider may recommend over-the-counter laxatives, such as magnesium hydroxide oral (Phillips’ Milk of Magnesia) or polyethylene glycol (Miralax).
- Anti-diarrheal medications. Over-the-counter medications, such as loperamide (Imodium A-D), can help control diarrhea. Your provider might also prescribe a bile acid binder, such as cholestyramine (Prevalite), colestipol (Colestid) or colesevelam (Welchol). Bile acid binders can cause bloating.
- Anticholinergic medications. Medications such as dicyclomine (Bentyl) can help relieve painful bowel spasms. They are sometimes prescribed for people who have bouts of diarrhea. These medications are generally safe but can cause constipation, dry mouth and blurred vision.
- Tricyclic antidepressants. This type of medication can help relieve depression, but it also inhibits the activity of neurons that control the intestines. This may help reduce pain. If you have diarrhea and abdominal pain without depression, your provider may suggest a lower than typical dose of imipramine (Tofranil), desipramine (Norpramin) or nortriptyline (Pamelor). Side effects — which might be reduced if you take the medication at bedtime — can include drowsiness, blurred vision, dizziness and dry mouth.
- SSRI antidepressants. Selective serotonin reuptake inhibitor (SSRI) antidepressants, such as fluoxetine (Prozac) or paroxetine (Paxil), may help if you are depressed and have pain and constipation.
- Pain medications. Pregabalin (Lyrica) or gabapentin (Neurontin) might ease severe pain or bloating.
Medications specifically for IBS
Medications approved for certain people with IBS include:
- Alosetron (Lotronex). Alosetron is designed to relax the colon and slow the movement of waste through the lower bowel. It can be prescribed only by providers enrolled in a special program. Alosetron is intended only for severe cases of diarrhea-predominant IBS in women who haven’t responded to other treatments. It is not approved for use by men. Alosetron has been linked to rare but important side effects, so it should only be considered when other treatments aren’t successful.
- Eluxadoline (Viberzi). Eluxadoline can ease diarrhea by reducing muscle contractions and fluid secretion in the intestine. It also helps increase muscle tone in the rectum. Side effects can include nausea, abdominal pain and mild constipation. Eluxadoline has also been associated with pancreatitis, which can be serious and more common in certain individuals.
- Rifaximin (Xifaxan). This antibiotic can decrease bacterial overgrowth and diarrhea.
- Lubiprostone (Amitiza). Lubiprostone can increase fluid secretion in your small intestine to help with the passage of stool. It’s approved for women who have IBS with constipation, and is generally prescribed only for women with severe symptoms that haven’t responded to other treatments.
- Linaclotide (Linzess). Linaclotide also can increase fluid secretion in your small intestine to help you pass stool. Linaclotide can cause diarrhea, but taking the medication 30 to 60 minutes before eating might help.