Fecal calprotectin: an inflammatory biomarker with emerging importance in the clinical laboratory

Recent advances in proteomics, metabolomics, bioinformatics, and related technologies have identified a plethora of biomarkers with promising clinical diagnostic utility; however, few have accomplished the difficult transition from the research laboratory to the clinical diagnostic laboratory. Hurdles include the inability to replicate promising research results in “real life” clinical laboratories, developing commercially practical formats, cost, and most importantly, providing results that are of clear use in daily clinical practice.

Patients presenting with persistent abdominal pain and diarrhea are common in clinical practice. Evaluation of these patients, assuming no alarm symptoms, can be difficult. Inflammatory bowel disease (IBD) is always a possibility and, while few will actually have IBD, the symptoms of irritable bowel syndrome (IBS) and IBD can overlap. Concern with a missed diagnosis of IBD leads many clinicians to request endoscopic evaluation. Most endoscopies are negative, with more than half of individuals with non-bleeding symptoms being diagnosed with non-organic disease, usually IBS.¹

Up to 70% of children and teenagers referred to a pediatric gastroenterology center for suspected IBD did not have the disease.²

Furthermore, although endoscopic procedures are relatively common, they are invasive, costly, require patient compliance with fasting and bowel preparation, involve sedation, are subjective, and can miss patchy inflammation.

The ability to non-invasively assess intestinal inflammation using biomarkers has been actively pursued for many years. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) give a generic indication of disease by measuring systemic responses, but lack specificity for gastrointestinal activity.Fecal markers are appealing indicators of intestinal inflammation since they originate from the intestinal mucosa and their presence in the stool is related to their level in the intestinal lumen.

Fecal calprotectin as a biomarker

Although fecal calprotectin (FC) has been known for almost 30 years, it has only fairly recently been attracting interest in the United States as a tool to help assess intestinal inflammation. Despite recognition of the value of FC measurement, its adoption in the United States has been slower than Europe due to limited availability, long turnaround times, and high send-out costs. A key reason for the recent surge in interest, in addition to accumulating studies documenting the practical value of FC in routine clinical practice, is the availability of a new FDA-cleared assay to clinical laboratories. This allows them more choices to perform the assay in their own facility.

Calprotectin is a calcium and zinc binding protein complex formed by S100A8 and S100A9 proteins. Historically, S100A8 and S100A9 have been known by a number of names including calgranulin A and B, as well as myeloid-related proteins 8 and 14. Calprotectin is an abundant protein, constituting about 5% of the total protein and up to 60% of the human neutrophil cytosolic protein.3 It is stable in stool for four to seven days at room temperature, allowing for easy collection and transport to laboratories for testing. Testing for FC requires only about 1 mg of stool and can be accomplished with an ELISA assay. Although calprotectin can be found throughout the body, FC is of most relevance to gastrointestinal disease since the calprotectin in stool is directly related to the quantity of neutrophils infiltrating the inflamed intestinal mucosa and consequently is a surrogate marker of inflammation.³

Using calprotectin to rule out IBD

IBS is the most commonly diagnosed gastrointestinal condition, affecting approximately 12% of the population in North America and up to 21% in South America.^4,5

Diagnosis commonly involves tests to rule out a variety of other diseases, and patients are very often referred for endoscopic evaluation to rule out IBD. Although less than 1% of patients with typical symptoms of IBS were found to have IBD in a prospective study of suspected IBS patients, endoscopy is still frequently ordered, resulting in considerable cost and low diagnostic yield.⁶

In contrast to patients with active IBD, patients with IBS have little or no mucosal inflammation. Since calprotectin has been clearly shown to correlate with intestinal inflammation, a negative FC result can help rule-out IBD in suspected IBS patients. A recent study examining the utility of CRP, ESR, FC, and fecal lactoferrin (FL) to exclude IBD concluded that utilizing both calprotectin and CRP (but not ESR or FL) could improve the confident diagnosis of IBS.⁷

The consequences of IBD are more severe than those of IBS, with most patients requiring surgery at one or more points in their life. For this reason, clinicians do not want to miss the diagnosis and will opt for endoscopic evaluation if they have a high index of suspicion. Using FC to evaluate 538 patients presenting with abdominal discomfort and subsequent endoscopic evaluation, it was found that 84% of 359 patients with FC <50 mg/kg had no lesions, while 87% of 179 patients with FC >50 mg/kg had significant lesions.⁸ A recent meta-analysis suggested that using FC levels as a screening tool to select patients most likely to need endoscopy could lead to a 67% reduction in the number of adults and 35% in the number of children needing endoscopy.⁹ An economic analysis of FC as a screening modality before endoscopy concluded that it is a cost-effective strategy in both adults and children for reducing the number of endoscopies.¹ In addition to saving money, pre-testing with calprotectin is attractive for patients who otherwise would need to spend time and money and endure an invasive procedure.

Monitoring mucosal inflammation

Achieving early mucosal healing in both ulcerative colitis (UC) and Crohn's disease is associated with less hospitalization, less surgery, and improved long-term clinical outcomes.10-12 Mucosal healing has therefore become an important endpoint for therapeutic intervention. Endoscopic evaluations, however, are subjective and correlate poorly with histologic inflammatory behavior.12 Furthermore, they are impractical for routine periodic assessment. The use of non-invasive markers for evaluation of mucosal healing is therefore of high interest. Fecal calprotectin appears useful to monitor the decline in inflammation and document effective therapeutic treatment.¹³

A recent study showed that patients with sustained deep remission had median FC consistently <40mg/kg during a 12-month follow-up period.¹³ Fecal calprotectin also appears useful to monitor patients for relapse. Rising calprotectin levels can indicate a coming relapse and can alert clinicians to restart or intensify therapy to avoid additional damage to a patient's mucosa that may occur during relapse. A study of patients prospectively followed for 12 months showed that those experiencing disease flares had median FC levels >300 mg/kg prior to the flare.¹³ In a study of 135 patients followed for reoccurrence of Crohn's Disease following surgery, FC was shown to be superior to the serum marker of inflammation CRP and to the Crohn's disease activity index (CDAI) in detecting early recurrence and monitoring the response to treatment.¹⁴

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FC is not specific for IBD, and it can be increased in a variety of conditions where there is intestinal inflammation or damage. For example, FC level can be very high in colorectal cancer as well as gastrointestinal infections, ulcers, and nonsteroidal enteropathy.¹⁵ The use of FC will continue to grow as more clinicians begin to understand its value for assessing patients with abdominal discomfort without the need of endoscopy in all cases. In the past, slow turnaround time has made FC results less useful for clinicians who cannot wait days for results to guide their management decisions. With the commercial availability of FDA-cleared assays, more clinical laboratories are now able to offer the assay with quick turnaround times. Reduction in unnecessary endoscopies by using FC to guide selection of patients for endoscopy will benefit both patients and health providers.

References

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