One way to test for Crohn's disease is with Full blood count test which will look for white blood cell levels (if there is a higher white blood count it can indicate that there is inflammation or an infection in the body e.g., bacteria) , platelet levels (as they can also show if there is inflammation in the body) and red blood cell levels (if you have few red blood cells it means you have less hemoglobin meaning less oxygen is carried around the body causing you to become anemic which is a symptom of IBD)