The Fecal Calprotectin Test (FCPT) is a non-invasive diagnostic tool used to measure inflammation within the gastrointestinal (GI) tract. It is frequently ordered when a patient presents with persistent symptoms such as diarrhea, abdominal pain, or changes in bowel habits. By quantifying a specific protein in a stool sample, the FCPT assesses the presence and degree of intestinal inflammation. Its primary purpose is to help determine if symptoms are caused by an inflammatory condition or a functional disorder.
Calprotectin: The Inflammatory Marker
Calprotectin is a protein released primarily by neutrophils, a type of white blood cell and part of the body’s immune system. This protein is a heterodimer composed of two calcium-binding proteins, S100A8 and S100A9. When inflammation occurs in the lining of the intestines, neutrophils migrate to the affected area. As these immune cells are activated or die off, they release their contents, including calprotectin, into the intestinal lumen, where it mixes with the stool.
The presence of calprotectin in the stool is a stable indicator of active inflammation in the GI tract. Because calprotectin is resistant to enzymatic breakdown within the gut, its concentration can be accurately measured in a collected stool sample. A higher concentration of this protein directly correlates with a greater migration of neutrophils and a higher level of inflammation. This makes the FCPT a valuable marker for the severity of intestinal inflammation.
Clinical Reasons for Ordering the Test
The FCPT is primarily used to distinguish between Inflammatory Bowel Disease (IBD) and Irritable Bowel Syndrome (IBS), two conditions with overlapping symptoms like abdominal pain and diarrhea. IBD (Crohn’s disease and ulcerative colitis) involves chronic inflammation and damage to the intestinal lining. In contrast, IBS is a functional disorder that does not cause inflammation or structural damage. A high calprotectin level strongly suggests that symptoms are caused by an inflammatory process like IBD.
Conversely, a normal calprotectin result suggests inflammation is unlikely and often points toward a functional disorder such as IBS. This distinction helps physicians avoid unnecessary invasive procedures, such as a colonoscopy, for patients whose symptoms are likely non-inflammatory. The test has high sensitivity and specificity for differentiating these two categories of bowel disorders.
For patients already diagnosed with IBD, the FCPT serves an ongoing role in monitoring the disease. Measuring calprotectin levels helps determine the current severity of inflammation and whether the disease is active or in remission. It is also used to monitor treatment effectiveness, as successful therapy should result in a decrease in calprotectin concentration. The test can also help predict the likelihood of a future IBD flare-up.
The Stool Sample Collection Process
The test requires a small stool specimen, typically collected by the patient at home using a specialized kit. The stool sample must not come into contact with toilet water, urine, or cleaning products, as these contaminants can affect the results. Patients are often provided with a collection container that may include an attached spoon or stick for scooping the sample.
The patient should collect a small, representative amount of the bowel movement and securely seal it in the provided container. Some containers may have a preservative liquid inside that should not be poured out. Patients should consult with their doctor about temporarily stopping non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen before the test, as these medications can cause a false elevation in calprotectin levels. The sealed sample needs to be returned to the clinic or laboratory as soon as possible, ideally within a few days.
Understanding the Test Results
Fecal calprotectin results are typically reported in micrograms per gram of stool (µg/g). Interpretation centers on identifying whether the protein level indicates a normal, borderline, or elevated level of intestinal inflammation. A result below 50 µg/g is considered normal and strongly suggests that symptoms are not due to an inflammatory process. This low level is often associated with conditions like Irritable Bowel Syndrome.
Levels in the moderate or borderline range (50 to 120 µg/g) may require closer monitoring or a repeat test. This moderate elevation can be caused by minor inflammation, certain medications, or other non-IBD conditions. A high level, often defined as above 250 µg/g, strongly suggests the presence of active inflammation, making IBD the likely cause.
The calprotectin test is not a final diagnosis in itself; it is a tool that measures inflammation. The physician must interpret the numerical result in the context of the patient’s symptoms, medical history, and other laboratory findings. A high result prompts the need for further diagnostic investigation, such as an endoscopy, to confirm the underlying cause.