Crohn’s and colitis: immune signals show up in blood a decade before diagnosis

Years before doctors give it a name, the immune system of a future Crohn’s or ulcerative colitis patient already behaves differently. Researchers reported at UEG Week 2026 that antibodies in the blood can serve as an early warning sign of inflammatory bowel disease, showing up as much as a decade ahead of diagnosis.

The team traced 500 people back in time. Of these, 200 were eventually diagnosed with Crohn’s disease, another 200 with ulcerative colitis, and 100 stayed healthy, matched to the others by age and sex. Their 2,000 serum samples dated from the moment of diagnosis and from about 10, four and two years earlier.

Each sample was tested for reactions to some 357,000 antigens linked to bacteria, viruses, food and the body itself, yielding 123,980 unique antibodies. Compared with the healthy group, those who later fell ill showed a clearly narrower range of antibodies, a difference visible in both conditions a full decade ahead.

The two diseases left separate fingerprints. Future Crohn’s patients reacted more strongly to herpesviruses and to flagellin, a bacterial protein, most notably when the disease turned out complicated or involved the ileum; their reactions to encapsulated bacteria faded as diagnosis neared. In ulcerative colitis, reactions to autoantigens and herpesviruses climbed, while those against encapsulated pathogens dropped.

Fed these profiles, machine learning models told future Crohn’s patients apart from healthy people with an AUC score of 0.90, against 0.84 for ulcerative colitis. Roughly ten years in advance, they also separated complicated Crohn’s from less severe forms, scoring 0.85.

“Finding these patterns so early points to the potential of antibody profiling to support earlier risk detection, distinguish between disease subtypes and help identify patients who may benefit from more intensive therapy as early as possible.”

Lead author Dr. Arno Bourgonje stressed the results are not ready for routine screening. The signatures must first be confirmed in independent, more varied groups followed over time, measured against genetic, clinical and other blood markers, and turned into a cheap, reproducible test that proves it improves outcomes for patients.