Fecal calprotectin (FC): What is it and what role does it play in Inflammatory Bowel Disease?

In Inflammatory Bowel Disease¹ there is an inflammation of the intestine that causes neutrophils to infiltrate to the inflamed area to act. In this inflamed environment, and to defend the body from the entry of bacteria from inside the intestine due to the disruption of the intestinal barrier and its increased permeability, neutrophils “commit suicide” in a process known as Netosis, forming NETs, structures with a network structure, whose function is to destroy the largest number of “intruding” bacteria as quickly as possible, so that they release all the intracellular contents to the outside. A very high percentage of neutrophil cytoplasm consists of calprotectin, which is a protein highly resistant to bacterial degradation and stable at room temperature for days. This calprotectin passes into the lumen of the intestine (since the intestinal barrier has lost its integrity) and is eliminated from the body through the feces, hence its name fecal calprotectin (FC). Thus, by measuring the levels of calprotectin in the stool, it is possible to determine, by its concentration, whether the patient is in an active flare or not, and even the severity of the disease.
The measurement of fecal calprotectin is very common in the diagnosis of IBD, to determine and evaluate the state of the disease. In addition, it is a biomarker that allows to analyze in a non-invasive way, the changes of a patient at the intestinal level over a long period of time.

How is a fecal calprotectin test performed and when is the best time to perform it?

Since the measurement of this protein is performed through the stool, it will be necessary to take a stool sample from the patient and analyze it. GETECCU’s recommendations for sample collection² are as follows:
It is recommended to collect a small amount of stool (approximately 3-5g) and deposit it in a collection container that is usually dispensed at the requesting center. This container does not require any specific treatment. The sample can be taken from any part of the stool, as it has been shown that CF is distributed homogeneously³ and at any time during the course of the disease.
As a precaution and to obtain a reliable result, a marked decrease in FC levels has been observed during preparation for colonoscopy⁴. Therefore, in case the patient is scheduled for one, caution should be taken to collect the sample before starting the colonic cleansing or several days after the test.

What does it mean when fecal calprotectin is elevated?

When CF is elevated in inflammatory bowel disease, it means that there is inflammation in the bowel. As a rule, high levels indicate bacterial infections, parasitic infections, colorectal cancer, or certain diseases that cause inflammation of the bowel, such as ulcerative colitis⁵ (UC) and Crohn’s disease⁶ (CD).

In both UC and CD this could mean that the disease is active and may be causing symptoms such as abdominal pain, diarrhea or bleeding as the immune system is fighting to decrease such inflammation in the gut.

Now that you understand what fecal calprotectin is, the most important thing is to trust your doctor, follow the prescribed treatment and communicate your symptoms so that he/she can plan the best strategy for managing your disease and perform the necessary tests at any given time.