Faecal calprotectin is a stool (poo) test. It may also be written as fecal calprotectin, stool calprotectin, FCP, FC or f-cal. Calprotectin is a protein that passes into the bowel in larger amounts when the bowel is inflamed, so the amount in a stool sample is a sign of inflammation in the gut.
Why doctors use it
Crohn’s disease and ulcerative colitis cause inflammation in the bowel; irritable bowel syndrome (IBS) doesn’t. So the test helps a doctor tell the two apart before deciding whether someone needs to see a specialist or have a colonoscopy. In the UK, NICE recommends it for this in adults with recent lower bowel symptoms when bowel cancer isn’t suspected, and in children with suspected inflammatory bowel disease (IBD) who have been referred to a specialist. IBD teams also use it to check how active inflammation is over time.
Reading the result
The result is usually a number in micrograms of calprotectin per gram of stool (µg/g), for example 15 micrograms/g. Some labs print it in mg/kg, which gives the same number (15 mg/kg is 15 micrograms/g). The lab compares it with a cut-off to decide whether it counts as raised. Most of the studies NICE assessed used a cut-off of 50 micrograms/g, but cut-offs differ between tests and labs, so use the range printed on your own report.
A raised result shows there is inflammation, but not what is causing it: other conditions can raise it too. A result under the cut-off makes IBD less likely, but your doctor reads it together with your symptoms and other tests.