The first step in diagnosing Crohn’s disease (CD) is a visit to a physician. The physician will compile a complete medical history and conduct a physical examination. Patients may be asked about the duration of their symptoms, any family history of CD, as well as their cigarette smoking habits. 

Blood tests and stool samples may also be required. Blood tests can identify low red blood cell counts (anemia), high white blood cell counts (which may indicate inflammation or infection) and nutrient levels. A stool sample analysis (fecal test) can rule out intestinal infections, which include symptoms similar to those of CD.

Because CD may involve any area of the digestive tract, there are a number of different imaging tests used to determine if a patient has the disease. In addition, these tests may be used to rule out evidence of infections or other diseases (e.g., colorectal cancer or diverticulitis) that may be causing the symptoms. These tests include:

• Barium x-ray. Organs are coated with a chalky substance (barium) that shows up on x-rays. Patients either drink the barium (for upper GI x-rays of the esophagus, stomach and/or small intestine) or have it administered via an enema (for lower GI x-rays of the large intestine). These x-rays allow physicians to identify any abnormalities within the digestive tract. Risks include low radiation exposure and possible perforation of the intestinal wall (which is very rare). Barium x-rays are not considered as reliable as an endoscopy for diagnosing CD because the x-rays may miss polyps and do not allow tissue samples to be taken.
  
  
• Conventional endoscopy. Examination using a small, flexible tube (with a light and camera) that is inserted through either the mouth or the anus and into the digestive tract. This procedure allows physicians to view the lining of the digestive tract and identify the severity and extent of any disease. In cases where the large intestine is being viewed, patients take a laxative prior to the procedure to cleanse the large intestine and are sedated during the procedure. A tissue sample (biopsy) may be taken for evaluation under a microscope. Color photographs may also be taken. Risks include perforation of the gastrointestinal wall and bleeding.
  
  Types of endoscopy used for patients with CD include:
  
  
• Colonoscopy. Used to view the entire large intestine.
  
  
• Sigmoidoscopy. Used to view the last two feet of the large intestine (the sigmoid colon) and the rectum.
  
  
• Esophagogastroduodenoscopy (EGD). Also called an upper endoscopy. An EGD is used to examine the esophagus, stomach and the first part of the small intestine (duodenum).
  
  
• Endoscopic retrograde cholangiopancreatography (ERCP). Used to examine the bile ducts in the liver and the pancreatic duct.
  
  
• Endoscopic ultrasound. Tube includes an ultrasound probe that takes below-the-surface images of the gastrointestinal lining. This is used to detect fistulas that develop near the anus in patients with CD.
  
  
• Capsule endoscopy. A new instrument, called a capsule endoscope, allows physicians to look for abnormalities in the small intestine. Patients swallow a capsule that contains a tiny camera, which transmits images of the small intestine to a recorder for later viewing. The camera passes painlessly in the patient’s stool. This may be especially helpful for areas of the small intestine that are hard to reach during a conventional endoscopy. In cases of severe intestinal obstruction, there is a risk the camera may become stuck in the intestine and this method is not used.
  
  
• CAT scans. Simultaneous x-rays taken from different angles. CAT scans provide more detailed images than standard x-rays. This may be used to look for any sign of intestinal obstruction, fistulas or abscesses that can result from CD. Risks include increased radiation exposure.