There’s no lab test your doctor can order to pinpoint IBS; diagnosis is done by interpreting symptoms. But she may recommend tests to rule out other conditions that can mimic IBS. These include stool checks, blood tests or even X-rays that check for problems such as inflammatory bowel disease (IBD), diabetes (which can slow down the movement of food in your digestive system), lactose intolerance, infections, or an over- or under-active thyroid. Your doctor may also suggest you have a colonoscopy. For this check, a long, thin tube with a light and tiny lens (called a colonoscope) is inserted into your colon to hunt for problems.

• One common test used to help diagnose IBS is a lower gastrointestinal series, which uses x-rays to rule out damage or obstructions in your large intestine.
• Gluten intolerance can cause IBS-like symptoms; a stool check lets your doctor look for tell-tale antibodies related to this health condition.
• A fasting blood sugar check is the standard test for diabetes. Your doctor may order one if he suspects diabetes has harmed nerves in your digestive system.
• To rule out lactose intolerance—the inability to digest milk sugars—your doctor may ask you to avoid dairy products for a week, to see whether symptoms improve.
• Your doctor may also order blood tests to rule out low iron, inflammation, infection, and parasites.

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