Irritable bowel syndrome can be quite hard to diagnose since this disorder is based solely on symptoms, without any alterations to the tissues. First of all, a complete medical history should be made and a physical exam conducted. IBS is diagnosed only if the symptoms began 6 months ago and recurred at least three times per month for the last 3 months. No other methods are usually conducted, unless the health care provider wants to screen the patient for other problems.
Additional methods are recommended if the patient also has fever, weight loss, rectal bleeding, or anemia, as well as family history of colon cancer, celiac disease, or irritable bowel disease. These methods may include:
- Stool test – during stool test a sample of stool is taken from the patient. The stool is collected into a special tightly sealed container. The stool sample should be brought to the laboratory no later than 12 hours after it was made. Stool sample shouldn’t be made after an enema or if the patient is taking drugs that contain iron, barium, or bismuth subcitrate. Before making a stool sample the person should follow a specific diet with moderate amount of fats, carbohydrates, and proteins. This test can determine the presence of blood, mucus, pus, parasites, and undigested food in the stool. In addition, the health care provider might also do a rectal exam, to exclude problems in the rectal area.
- Blood tests – including:
- Full blood examination – could be used to detect anemia, allergic reaction, inflammation, along with a number of other conditions
- Erythrocyte sedimentation rate – can sometimes be useful in diagnosing auto-immune diseases, inflammatory bowel disease, chronic kidney diseases, which should be differentiated from irritable bowel syndrome.
- Liver function tests – determine the ratio and levels of aspartate aminotransferase and alanine aminotransferase. These tests can detect damage to liver as well as specific conditions including alcoholic hepatitis, cirrhosis, hepatocellular carcinoma, and viral hepatitis.
- Serological testing for celiac disease – it is important to rule out celiac disease when diagnosing irritable bowel syndrome, since a number of symptoms caused by celiac disease are quite similar to IBS.
- Ultrasound of the abdominal region – is used to exclude gallstones, pancreatitis, and malformations of bile and pancreatic ducts. These conditions can also cause pain and discomfort and should be differentiated from IBS.
- Esophagogastroduodenoscopy – is used to exclude tumors of the upper part of the intestinal tract and peptic ulcer disease.
- Hydrogen breath testing - is a non-invasive test that is performed after fasting for 8 to 12 hours. It can be used to determine if the patient suffers from lactose or fructose malabsorption. This test is based on the fact that when a certain sugar is not absorbed in the small intestine, it is getting metabolized by the bacteria which produce hydrogen in some patients and methane in others (some patients don’t produce any gas at all, or it is some other gas, which cannot be detected). In order to detect fructose malabsorption, about 20 grams of fructose is given to the patient. Then the readings are taken every 15, 30, or 60 minutes for the period of 3 hours, during which the patient blows into a special device, which captures the breath samples. Similarly, to detect lactose malabsorption, the patient is given 20 or 25g of pure lactose. If the hydrogen or methane levels in the breath rise by 12 ppm over the preceding value, the test is considered to be positive. Small Bowel Bacterial Overgrowth Syndrome can also be detected using this test. In this case 75 to 100 grams of dextrose or 10 grams of lactulose are given to the patient and the readings are taken for 3 to 5 hours to detect the rise in hydrogen or methane. If the rise happened in the first two hours – then the bacteria are located in the small intestine, followed by a large peak (colonic response).
- Lower GI series – is method of visualizing the large intestine using X-ray. Anesthesia is not necessary for this procedure since it is completely painless, though sometimes slightly uncomfortable. Before the test the patient is usually asked to follow a liquid diet for 1 or 2 days. Right before the test an enema is used to clear out the content of the large intestine. During this procedure the person is lying on the table and a flexible tube is inserted into the patient’s anus. The large intestine is then filled with barium, which enables the radiologist to clearly see any changes to the internal structure of the large intestine.
- Colonoscopy and flexible sigmoidoscopy – are similar methods with the only difference is that colonoscopy is used to view the entire colon, while sigmoidoscopy is only used to view the rectum and the lower part of the colon. Before the test the patient will follow a number of instructions including having a clear liquid diet for a couple of days and taking a laxative the night before the test. Before colonoscopy or sigmoidoscopy is performed, an additional enema might be needed. Additionally, a light anesthesia is used in order to help the patient relax during colonoscopy. The colonoscope is then inserted into the patient’s anus. A small camera, attached to the end of the colonoscope, allows the medical practitioner to view the intestinal lining. Colonoscope can also be used to take a biopsy (taking a piece of the intestinal lining to view it later under a microscope). The patient doesn’t feel anything when the biopsy is being taken. Common side effects of colonoscopy are bloating and cramping. Also, the patient shouldn’t drive right after colonoscopy since anesthesia wears off only after 3-4 hours.