There are 3 different forms of IBS: Diarrhea-predominant (D-IBS), constipation-predominant (C-IBS), and alternating constipation and diarrhea (A-IBS). Symptoms of the different forms include:
- D-IBS: abdominal discomfort or pain, urgency and diarrhea
- C-IBS: abdominal discomfort or pain, bloating and constipation
- A-IBS: Intermittent symptoms of D-IBS and C-IBS
IBS is a diagnosis of exclusion, which means that organic diseases, infection, or other cause of the symptoms must be ruled out. In 1988 a group of physicians defined criteria to more accurately diagnose IBS. Known as the "Rome Criteria," this set of guidelines that outlines symptoms and applies parameters such as frequency and duration make possible a more accurate diagnosis of IBS. The Rome Criteria is still evolving, and may be updated as more is learned about IBS.
The Rome criteria are:
- Three months of continuous or recurring symptoms of abdominal pain or irritation that
- May be relieved with a bowel movement,
- May be coupled with a change in frequency, or
- May be related to a change in the consistency of stools.
- Two or more of the following are present at least 25 percent (one quarter) of the time:
- A change in stool frequency (more than 3 bowel movement per day or fewer than 3 bowel movements per week)
- Noticeable difference in stool form (hard, loose and watery stools or poorly formed stools)
- Passage of mucous in stools
- Bloating or feeling of abdominal distention
- Altered stool passage (e.g. sensations of incomplete evacuation, straining, or urgency)
Symptoms in the Rome Criteria are not the only indicators of IBS. Extra intestinal symptoms include:
- Full sensation after even a small meal
In addition to using the Rome Criteria, physicians may run several tests to ensure that there is no inflammation or infection in the body.
Blood tests. A blood test may be used to determine the white blood cell count or if anemia is present. A high white blood cell count gives physicians an indication that inflammation is taking place somewhere inside the body. Inflammation is not a symptom IBS.
Fecal occult blood test. This test can detect bleeding from almost anywhere in the digestive tract, even if it is not visible to the naked eye. The stool collection may be done at home without any discomfort and returned to the physician or laboratory for testing. Blood in the stool is not a symptom of IBS.
Stool culture. A physician may want to rule out other causes for diarrhea, such as a bacterial infection or parasite, with a stool culture. Stool must be collected into a specimen jar and brought to a laboratory for testing in a culture. If any bacteria are found, the scientists can test it to determine what species it is and how best to treat it.
Barium enema. A barium enema (or lower gastrointestinal series) uses barium sulfate and air to outline the lining of the rectum and colon. The barium is given in an enema which is then 'held' inside the colon while X-rays are taken. Intestinal abnormalities may appear as dark silhouettes or patterns along the intestinal lining on the X-ray.
Sigmoidoscopy. A sigmoidoscopy is a way for a doctor to examine the last one third of the large intestine. A flexible viewing tube with a lens and light source on the end, called a sigmoidoscope, is used. A biopsy may be taken during the procedure, which will be tested to help the physician determine the cause of any inflammation.
Colonoscopy. A colonoscopy is used to examine the inside of the colon beyond the areas a sigmoidoscopy can reach. This test uses a colonoscope: a flexible tube with lenses, a tiny TV camera and a light at the end. Biopsies are taken during the test and patients are normally sedated or given "twilight sleep" so that they do not feel any pain.
Other tests may be used by physicians as needed to diagnose IBS, or rule out other potential diagnoses.