how is it possible?

The fecal calprotectin stool test can measure inflammation markers and blood work also shows inflammation, both of which can point to Crohn's. There are also blood tests called Serology 7 that look at a bunch of different indicators for Crohn's. Usually, doctors don't confirm the diagnosis without a positive biopsy on colonoscopy, or clearly visualized disease with the pill cam test. I hope that helps