Your doctor will likely diagnose Crohn's disease only after ruling out other possible causes for your signs and symptoms. There is no single test to diagnose Crohn's disease. Your doctor will likely use a combination of tests to help confirm a diagnosis of Crohn's disease, includes
Lab tests:
• Blood tests: Your doctor may suggest blood tests to check for anemia — conditions in which there aren’t enough red blood cells to carry adequate oxygen to your tissues — or to check for signs of infection.
• Stool studies: You may need to provide a stool sample so that your doctor can test for hidden (occult) blood or organisms, such as parasites, in your stool.
Procedures:
• Colonoscopy: This test allows your doctor to view your entire colon and the very end of your ileum (terminal ileum) using a thin, flexible, lighted tube with a camera at the end. During the procedure, your doctor can also take small samples of tissue (biopsy) for laboratory analysis, which may help to make a diagnosis. Clusters of inflammatory cells called granulomas, if present, help essentially confirm the diagnosis of Crohn's.
Courtesy: Mayo Clinic