context: Your stomach has been feeling crummy for a while now. That pain and cramping comes and goes, but even after a few months, you just can't shake it. You've heard of something called IBS -- or irritable bowel syndrome. Could it be what you've got? And how will your doctor find out? There are some tests that help figure out what's going on, including a new blood test. But the most common way your doctor makes a diagnosis is with a bit of detective work. Your doctor will ask for the details of what's bothering you. He'll compare that with a set of symptoms known as the Rome IV Criteria. To meet the standard, your belly pain needs to have been a problem for at least 6 months. And in the last 3 months, you'll have noticed it at least 1 day per week. You also need to have two of these symptoms: Your belly pain is related to a bowel movement. When you have pain or discomfort, your bowel movements are either more or less frequent than usual. Your stools have changed in appearance and are harder or softer than usual when you have pain or discomfort. If this is what you're going through -- and you don't have any red flags for another disease, like blood in your stool, unexplained weight loss, or fever -- your doctor may not need to check further. He may be ready to diagnose you with IBS and start treatment. But if your symptoms include diarrhea, or if they only started after you turned 50, you may need tests to look for other possible causes. And if you have a family history of other stomach diseases, your doctor will want to rule those out. There is no definitive diagnostic laboratory test for IBS. The purpose of laboratory testing is primarily to exclude an alternative diagnosis. All patients with suspected IBS, a complete blood count must be done. The test can help confirm the disease if your main symptom is diarrhea. But scientists are still studying how well the test works when constipation is your chief complaint. One thing to keep in mind: Sometimes the results are inconclusive. Your doctor may need to do more tests to find the root cause of your symptoms. Your doctor has some other ways to see why you're not feeling so great. Sometimes other conditions are to blame. There are tests that can help rule them in or out. For instance, he may check to see if your body isn't able to absorb or digest certain ingredients, like dairy or a simple sugar called fructose. One way to find out is to see if your symptoms get better if you take them out of your diet. You may also need to get a blood test to look for signs of Celiac disease, which happens when your body can't handle gluten, a protein found in wheat, barley, and oats. Your doctor might order a colonoscopy, an exam that looks for polyps in your large intestine. Another option may be a test called a flexible sigmoidoscopy. During both procedures, your doctor puts a narrow, flexible tube with a camera into your rectum. He moves it into your body to examine part or all of the large intestine. During the colonoscopy, he may collect small sections of tissue from the large intestine and examine them under a microscope. It won't show if you have IBS, but you may learn if you've got other conditions like colitis or inflammatory bowel disease. Another way your doctor might want to look at your large intestine is with an X-ray called a lower GI series, or barium enema. For this test, he puts a flexible tube into the rectum and fills the large intestine with barium, a liquid that lights up on X-rays. Finally, you may be asked to save a stool sample to be tested for blood, infection, or parasites. Your doctor will give you a container and instructions on where to send or take the kit for analysis. All this testing can seem like a nuisance, but it's vital if you want to find out what's causing your stomach problems. Once you've got a diagnosis, your doctor can start the right treatment and put you on the road to relief.