Fecal calprotectin

Fecal calprotectin is a stool test that measures a protein called calprotectin to check for inflammation in the intestines. The idea behind it is simple: when the gut is inflamed, the immune system sends white blood cells called neutrophils to the area, and those cells release calprotectin, which then mixes with the stool. A higher amount in the stool points to more inflammation (MedlinePlus).

The test is done from a stool sample you collect, so it is non-invasive, which is part of why it is so useful early on.

What it helps answer

Its main job is to help tell apart two things that can feel similar but are very different underneath: inflammatory bowel disease (IBD, which includes Crohn's disease and ulcerative colitis and does involve inflammation) and irritable bowel syndrome (IBS, which does not). Normal or low levels usually mean the intestines are not inflamed; high levels usually mean they are (MedlinePlus).

A guide, not a verdict

NICE recommends faecal calprotectin as an option to support the choice between IBD and IBS in adults with recent-onset lower bowel symptoms, when specialist assessment is being considered and cancer is not suspected. A common cut-off is 50 micrograms per gram, but it is important to know this is a signal, not a diagnosis: some people with IBS can have raised levels, and some people with IBD can have lower ones (NICE). That is why a raised result usually leads to more tests, such as a colonoscopy, rather than a final answer on its own.