Blood test predicts Crohn's disease years before symptoms appear

A blood test can now identify people at risk of developing Crohn's disease nearly two and a half years before symptoms start. The discovery, from researchers at Sinai Health in Toronto, opens a door that's been closed for decades: the chance to intervene before the disease damages the gut.

Crohn's disease is typically diagnosed only after significant intestinal damage has already occurred. By then, patients are often dealing with chronic pain, inflammation, and complications that reshape their daily lives. This test changes that timeline.

The immune signal that comes first

The test looks for antibodies against flagellin, a protein found on certain gut bacteria. Dr. Ken Croitoru and his team at the Lunenfeld-Tanenbaum Research Institute found that some people develop an unusually strong immune response to this protein years before Crohn's actually develops. The immune system is essentially sounding an alarm about bacteria that should be harmless.

In healthy people, gut bacteria live in balance with the body. But in Crohn's disease, something goes wrong — the immune system begins attacking bacteria it should tolerate. Croitoru's team wanted to know whether this immune misdirection shows up in healthy people who are about to get sick.

They tracked 381 first-degree relatives of people with Crohn's disease (people with a genetic predisposition) over several years. Of the 77 who eventually developed Crohn's, 28 had elevated flagellin antibodies in their blood years earlier — more than one third of the group. The strongest signals appeared in siblings, suggesting that shared environmental factors matter alongside genetics.

From prediction to prevention

This isn't just about earlier diagnosis. The findings suggest a path toward prevention. "We have all these advanced therapies now, but patients' responses are partial at best," Croitoru said. "We haven't cured anybody yet, and we need to do better."

The work builds on research from the University of Alabama showing that Crohn's patients have high antibody levels against flagellin from Lachnospiraceae bacteria. What's new is the evidence that healthy people who go on to develop Crohn's show the same immune response first — sometimes years in advance.

This distinction matters. It suggests the immune reaction isn't a symptom of the disease, but possibly a trigger. Understanding what sets off that trigger could lead to ways to prevent it.

Dr. Sun-Ho Lee, a gastroenterologist on the team, is already exploring the next step: designing a flagellin-directed vaccine for high-risk individuals. The idea is to retrain the immune system before it causes damage.

The research comes from the GEM Project, a long-term international study that has followed over 5,000 healthy relatives of Crohn's patients since 2008, collecting genetic, biological, and environmental data. Having 130 participants develop the disease over that time gave researchers something rare: a window into how Crohn's actually begins.

Further validation studies are underway. If the test proves reliable in larger populations, it could reshape how gastroenterologists approach a disease that affects roughly 3 million people in North America alone.