The best way to tell this is via Colonoscopy. Other tests include MRI-E, CT Scan with Contrast, Pill Cam and others. They can also check your blood levels (C Reactive Protein etc.). Also, from your explanation of symptoms.
For example, on a colonoscopy, someone may have strictures, fistulas, lots of damage to the intestine etc. This would be a sign of more severe disease. Another way to tell is by the number of surgeries you need and the amount of medical care. Basically, it can definitely be determined over time.
Hope this helps.
Best,
Matt (Team Member)