The differential diagnosis for inflammatory bowel disease (IBD) includes irritable bowel syndrome (IBS). While the clinical presentation is similar, IBD is an inflammatory disease, while IBS is a noninflammatory disease. The usual approach is to develop a comprehensive clinical picture and family history, but without endoscopy or biopsy, it's virtually impossible to distinguish whether the patient is suffering from IBD or IBS. The stool calprotectin test (Calprotectin, Feces; Test ID: CALPR) offers a noninvasive option to assess for localized inflammation, potentially eliminating the need for biopsy in patients with IBS.

Presenter

Transcript

Our speaker for this program is Dr. Melissa Snyder, a Professor of Laboratory Medicine and Pathology at Mayo Clinic, as well as a consultant in the Clinical Biochemistry Laboratory. Dr. Snyder discusses the use of calprotectin as an indicator of inflammation in the gastrointestinal tract. The calprotectin test (CALPR / Calprotectin, Feces) can be used to exclude inflammatory bowel disease from the diagnosis of adult patients with irritable bowel syndrome.Welcome to Mayo Medical Laboratories Hot Topics. These presentations provide short discussion of current topics and may be helpful to you in your practice.

Thank you for that introduction.

Disclosures

Before beginning this presentation, I want to acknowledge that I have been a member of the Scientific Advisory Committee for Inova Diagnostics, the manufacturer of the calprotectin immunoassay.

Utilization Management

Utilization management is an important topic for many institutions. While viewing this presentation, take some time to consider a few points, including how this testing might be used in your practice? When the tests should be used? And how the results from this testing might impact patient management.

General Characteristics of IBD

Inflammatory bowel disease or IBD is a chronic inflammatory disease that affects the gastrointestinal system. IBD actually consists of 2 distinct diseases–ulcerative colitis and Crohn’s disease. Although both are classified as IBD, they each have unique characteristics, some of which are shown in this figure. Ulcerative colitis primarily affects the colon and/or the rectum, which is shown in the figure as the reddened areas. Ulcerative colitis also is characterized by diffuse inflammation, which ultimately leads to distortion of the crypt architecture, which can be seen on biopsy evaluation. In contrast, Crohn’s disease can affect any portion of the GI tract. Also, with Crohn’s disease, the lesions tend to be more discontinuous and transmural in nature, leading in some cases to a thickened bowel wall with evidence of fissures.

Clinical Manifestations of IBD

There are a variety of clinical symptoms associated with IBD, and these can classified as either intestinal or extraintestinal. Ulcerative colitis and Crohn’s disease each have some unique gastrointestinal manifestations, which can provide clues to the differential diagnosis. Ulcerative colitis can be associated with GI symptoms of diarrhea, bloody stool, lower abdominal cramping, and sometimes a perforated bowel. In contrast, Crohn’s disease is more frequently characterized by abdominal pain, fistulas, perianal involvement, and intestinal obstruction. With regard to the extraintestinal manifestations, for both Crohn’s disease and ulcerative colitis, these are often general and nonspecific, and may include arthralgias, oral ulcers or other cutaneous symptoms, fever, weight loss, and fatigue.

Differential Diagnoses and IBD

The diagnosis of IBD can be challenging, as ulcerative colitis and Crohn’s disease may have a clinical presentation similar to that of infection, malignancy, or irritable bowel syndrome, also referred to as IBS. IBD, infection, and malignancy are all inflammatory conditions, and are associated with activation of specific parts of the immune system. In contrast, IBS is considered to be a noninflammatory condition. This is an important distinction, particularly as we consider the role of calprotectin.

Diagnostic Evaluation for Suspected IBD

The diagnostic evaluation for suspected IBD begins with a thorough clinical evaluation, with a focus on gastrointestinal and extragastrointestinal symptoms and family history. The next step is usually an endoscopy with a biopsy evaluation. The purpose of this procedure is to assess for inflammation and document the location and characteristics of the immune response. Imaging studies may also be used, although this is generally for evaluation of the inflammation and not necessarily for diagnosis. And lastly, there is laboratory testing. The laboratory testing for IBD involves both serum and stool samples.

Laboratory Testing for Suspected IBD

The purpose of serum testing includes assessing for systemic inflammation, such as through measurement of C-reactive protein, and evaluating for malabsorption, including iron-deficient anemia, vitamin deficiency, and low protein concentrations. In addition, serology testing may be considered, specifically anti-Saccharomyces cerevisiae antibodies and perinuclear antineutrophil antibodies, or pANCA. Due to low sensitivity, serology testing is not useful for diagnosis of IBD. For most patients, the diagnosis of IBD and the differentiation between ulcerative colitis and Crohn’s disease can be made on the basis of clinical history and endoscopy with biopsy. For a small subset of patients with IBD, the distinction between ulcerative colitis and Crohn’s disease may not be as clear. For these patients, serology testing may be helpful. Patients with Crohn’s disease tend to be positive for anti-Saccharomyces cerevisiae antibodies and negative for pANCA. In contrast, patients with ulcerative colitis are more likely to be positive for pANCA and negative for Saccharomyces antibodies. It is for this reason that this testing is generally performed as a panel, with the results being helpful for differentiating between ulcerative colitis and Crohn’s disease for the group of patients in whom this distinction cannot be made using endoscopy.

In addition to serum testing, stool evaluation is a critical diagnostic component for patients with suspected IBD. Stool testing is useful for ruling out infections as well as for assessing for the presence of occult blood. In addition, through the use of fecal calprotectin, it is possible to determine if there is localized inflammation within the gastrointestinal tract. It is for this reason that we will now focus on calprotectin for the remainder of this hot topic

Introduction to Calprotectin

Calprotectin is a heterodimer of the calcium-binding protein S100A8 and A9. It is one of the most abundant proteins in neutrophils, accounting for almost 60% of the cytosolic protein content. An inflammatory response in the gastrointestinal system is associated with neutrophil migration. At the site of inflammation, neutrophils are activated, which leads to release of calprotectin. The calprotectin then accumulates in the fecal material and is excreted from the body.

Diagnostic Application of Calprotectin

Numerous studies have addressed the diagnostic utility of calprotectin related to IBD. In a recent meta-analysis, several studies which looked at the ability of calprotectin to distinguish IBD from other GI diseases were evaluated. This figure shows the sensitivities and specificities of calprotectin in both adult and pediatric populations in the various studies included in the meta-analysis. Overall, most studies show that calprotectin has a sensitivity of greater than 90% for the diagnosis of IBD. However, in terms of specificity, there was much more variability, especially in the pediatric populations.

A second meta-analysis, published in 2014, looked specifically at studies in which calprotectin was evaluated for diagnosis of pediatric IBD. The results are very similar to the previous meta-analysis–most studies found that calprotectin had sensitivities above 90% for the diagnosis of pediatric IBD. In addition, there was significant variation in the specificities from the individual studies, ranging from 60% to 90%. The high sensitivity of calprotectin led some researchers to evaluate whether this test could be used to exclude IBD as a diagnosis. In their study, they found that a calprotectin result of less than 40 micrograms/gram was associated with a less than 1% chance of having IBD. Most of the data in the literature indicate that calprotectin is a sensitive marker for IBD, such that a low fecal concentration can be used to rule out the diagnosis. However, the relatively poor specificity of calprotectin indicates that an elevated value is not diagnostic for IBD. Why is this the case?

Diagnostic Limitations of Calprotectin

Remember that neutrophils localize to the GI system as part of any immune response. This localization is not specific for the cause of that inflammatory response. We know that an inflammatory response occurs in IBD. However, inflammation within the GI system can also be found in celiac disease, infection, colorectal cancer, and even with the use of nonsteroidal anti-inflammatories. In other words, calprotectin must be viewed as a nonspecific marker of inflammation within the gastrointestinal system, and not as a diagnostic marker for an individual disease.

Diagnostic Algorithm Using Calprotectin

Despite the issue with specificity, the high sensitivity of this test has led some to propose a diagnostic algorithm that incorporates calprotectin. The algorithm starts by measuring fecal calprotectin in a patient who has symptoms consistent with an inflammatory GI condition. In this algorithm, a fecal calprotectin result less than 50 micrograms/gram would be more consistent with a noninflmamtory condition, such as IBS. In comparison, a calprotectin result greater than 150 micrograms/gram would be consistent with an inflammatory GI disease, which might include IBD, infection, or malignancy. For these patients, further evaluation including endoscopy or colonoscopy might be considered. For a borderline calprotectin result between 50 and 150 microgram/gram, it would be important to exclude possible causes of GI inflammation, such as the use of nonsteroidal anti-inflammatories. After waiting for a period of time, possibly 1 to 2 weeks, testing for calprotectin could be repeated. At this time, if the calprotectin is still greater than 50 micrograms/gram, then a colonoscopy might be indicated. However, if the calprotectin has decreased and is now below 50 micrograms/gram, a noninflammatory condition is more likely. Although the specific cutoffs may vary, the take home message is that a low fecal calprotectin result is indicative of a noninflammatory condition, while an elevated calprotectin is consistent with some type of inflammatory GI disease.

Calprotectin and IBD Summary

In summary, we can see that, related to diagnostic utility, a negative fecal calprotectin result is useful for excluding IBD and other inflammatory conditions as a diagnosis. In contrast, an elevated calprotectin result is consistent with the presence of gastrointestinal inflammation and should trigger further evaluation. This is the primary diagnostic limitation of fecal calprotectin–that an elevation is not specific for a single disease, and is only a marker of neutrophil activation within the gastrointestinal system.

References

This slide includes several references to which I referred to during this presentation. These references include a number of studies with more detailed information related to the diagnostic utility of fecal calprotectin.