The clinical usefulness of faecal calprotectin measurements in primary and secondary health care is discussed
Ingvar Bjarnason MD MSc FRCPath FRCP DSc
Department of Gastroenterology and Colorectal Surgery, King’s College Hospital, London, UK
Innovations in gastroenterology take variable times to filter through to clinical practice. In general, the availability and use of biochemical diagnostic screening procedures, especially in gastroenterology, has declined substantially in the last 20 years while the use of endoscopy has increased. The reasons for these changes are numerous, including increasing demand for colonoscopies due to a national screening programme for colorectal cancer in the at-average risk population, dedicated rapid access pathways for patients thought to be at high risk of colorectal cancer (two week waits) and the increasing time that the procedure take as endoscopy units increasingly offer mucosal and submucosal resection of colonic lesions that may take up to four times longer than a diagnostic colonoscopy. At the same time, increased demand for all aspects of endoscopy in the UK is problematic because there are already long waiting times for procedures in most hospitals.
A new biochemical test
It is now just over 15 years since the first reports of the clinical usefulness of a new biochemical test – measurement of faecal calprotectin – as a diagnostic screening test. Early results indicated that this test had the potential to revolutionise early decision-making with regards to the more expensive invasive investigational procedures: that is, that it could be used as a gate-keeper to colonoscopy and thereby reduce waiting times and costs.(1,2) Furthermore, and unlike endoscopy, the test, it was suggested, had the potential to predict the prognosis of certain diseases and hence guide and improve treatments.(3) Today it seems that all these promises have been fulfilled as demonstrated by numerous publications on the sensitivity and specificity of the test from all over the world. However, unlike most European countries, few hospitals in the UK have taken up the test. Here we provide a short up-to-date review of the clinical usefulness of calprotectin measurements in primary and secondary care.
Calprotectin is a protein that is selectively produced in substantial quantities by neutrophils. It is not degraded to any significant extent by intestinal bacteria so the amounts measured in stools accurately reflect the amount of neutrophils infiltrating the gastrointestinal mucosa. Neutrophils are synonymous with acute inflammation, so the test is inflammation- and not disease-specific. This is very important. Endoscopy with biopsy provides a diagnosis whereas faecal calprotectin is a functional test, reflecting and quantitating inflammation.
As it turns out, there is a low-grade influx of neutrophils to the gastrointestinal mucosa in normal healthy people, reflecting the fact that luminal bacteria and other luminal aggressors are local irritants. However, almost all intestinal diseases are associated with a breach in mucosal integrity. This, in turn, leads to increased intestinal permeability with a consequential acute inflammatory reaction as bacteria gain access to the mucosa.
This inflammation is captured by measurements of faecal calprotectin. Measurement of calprotectin simply involves obtaining a few milligrams of stool and the assay is by enzyme-linked immunosorbent assay (ELISA). The original kits contained sufficient number of wells to measure 40 individual faecal samples at a cost of £10–15 each excluding labour cost. More recently, single quantitative assays are available, allowing estimation of calprotectin levels within 15 minutes of receiving the sample and as the patent has expired, the price of kits has become more competitive.
The potential use of faecal calprotectin measurements can be summarised as:
- Diagnostic screen. If of sufficient sensitivity, it has the potential as clinical screening tests to determine whether more invasive investigations are warranted. This is the main use of the tests in clinical practice
- Assessing responses to treatment. This is one of the main challenges in inflammatory bowel disease (IBD) where the aims of treatment are increasingly mucosal healing
- Providing prognostic information. Raised faecal calprotectin can predict an imminent clinical relapse of IBD, in which case treatment can be initiated to avoid the clinical relapse
- For research. A number of intestinal diseases have been discovered as a consequence of acting on findings of increased intestinal permeability and inflammation in situations where no disease were thought to exist.
Proximal small bowel diseases are relatively uncommon and are easily identified by serum transglutaminase assay (coeliac disease) or by capsule enteroscopy. However, the main burden of intestinal disease is in the distal small bowel and colon, where there are abundant bacteria that cause inflammation consequent to a breach in mucosal integrity caused by non-functional diseases. Lower gastrointestinal symptoms account for approximately 20% of general practitioners’ workloads and over 60% of referrals to hospital-based gastroenterologists and colorectal surgeons.
The majority of patients with lower gastrointestinal symptoms have irritable bowel syndrome (IBS), and these account for 40% of patients referred from primary care to gastroenterology departments. IBS has various presentations, but despite clinical guidelines and ROME criteria advocating making a positive diagnosis of IBS with minimal invasive procedures, GPs send these patients to specialists in order not to miss significant colonic disease. Consequently, most gastroenterologists and trainees subject these patients to colonoscopy or other equally expensive imaging procedures.
Given that inflammation is the common denominator of all significant colonic disease, and not IBS, prompted research to assess the potential of faecal calprotectin in order to discriminate between organic disease and IBS in a patient group referred to the department of gastroenterology at King’s College Hospital. A total of 602 consecutive patients had faecal calprotectin testing carried out along with documentation of the ROME criteria for IBS. Overall, faecal calprotectin had an 89% and 79% sensitivity and specificity, respectively, for detecting organic intestinal disease.(4) The sensitivity of positive ROME criteria for IBS in this study was an impressive 85% with a specificity of 71%. However, the combination of a normal faecal calprotectin and positive ROME criteria had a predictive value for IBS approaching 100%.
Although 15% of patients with IBS had minimal elevations of faecal calprotectins, the main use of the test as described is in the whole group of patients with normal calprotectins in whom there was a very low likelihood of detecting organic disease, and it is precisely this group of patients that do not require colonoscopy or other imaging. If adhered to, this translates to yearly savings of hundreds of thousands of pounds for hospital-based gastroenterologists because these patients do not require colonoscopy.
Furthermore, when applied in primary care, there is perhaps a 40% reduction in GP referrals to the hospital-based gastroenterological services. If used appropriately, it provides the basis for a safe one-stop gastroenterology outpatient clinic.
The above study and those from other groups show that patients with clinically active ulcerative colitis and Crohn’s disease have faecal calprotectin levels that are 10-100-fold greater than healthy controls with a sensitivity approaching 100%.(1,4,5)
Another diseases associated with increased faecal calprotectin is long-term non-steroidal anti-inflammatory drug (NSAID) ingestion (70% have NSAID-enteropathy), which is associated with small bowel bleeding contributing to anaemia. Intestinal infections with Salmonella, Campylobacter and Shigella (over 90% have raised faecal calprotectin) yield abnormal test results.6 The test is indeed useful in patients with traveller’s diarrhoea, in order to distinguish between food infection and non-inflammatory food poisoning or common traveller’s diarrhoea as the prognosis of these conditions differ markedly. Most patients with diverticulosis (as opposed to diverticulitis) have normal faecal calprotectin, and a normal calprotectin in patients with suspected diverticulitis has the potential of avoiding a computed tomography scan of the abdomen in search of sigmoid diverticulitis.
Most interestingly, patients with colorectal cancer have abnormal test results.(7) The consensus from a number of studies is that the test shows a detection rate in excess of 90% in patients with colorectal cancer, irrespective of the stage of the disease; this compares with a 40% detection rates faecal occult blood testing. However, its use for colorectal cancer screening is associated with an unacceptable (as judged by the funders in the UK) increased requirement for colonoscopy. However, other developed countries, such as the USA and Scandinavia, offer colonoscopy as a first-line investigation for colorectal cancer screening.
A proportion of patients with coeliac disease or diabetic diarrhoea have raised faecal calprotectin, perhaps reflecting small bowel bacterial overgrowth.
The potential of faecal calprotectin in paediatric practice, where there is a reluctance to employ invasive diagnostic techniques, is clear. IBD is not particularly common in children but the same proportion of paediatric IBD patients has abnormal results as the adults,8 suggesting that it can act as a gate-keeper for more invasive procedures in this patient group.
The test can therefore be used as a screen for gastrointestinal normality and thereby avoids a large number of colonoscopies if used properly.
Assessing response to treatment
Faecal calprotectin is raised in the vast majority of patients with acute exacerbation of IBD and levels correlate with histopathological indices of acute inflammation. It has therefore been used to determine the appropriateness of starting medical treatment and assess responses to such treatment. Of particular interest are those patients who have an incomplete clinical response and a significant drop from a high to low faecal calprotectin This should alert one to the possibility of co-existing IBS (thus avoiding a step-up in treatment) or indeed stricturing disease (which requires surgery). However, a persistently high calprotectin in a symptomatic IBD patient that is receiving treatment is an indication to step-up the treatment.
The most interesting use of calprotectins in IBD relates to the decision to treat those who are asymptomatic but who have significant intestinal inflammation. This equates to the aim of mucosal healing and is currently the most promising approach to altering the natural history of the disease. Unfortunately for the IBD patients, most of the affordable drugs used for this purpose are off patent, so pharmacologic support for research studies assessing this is unlikely to be forthcoming.
Providing prognostic information
The causes of clinical relapse of IBD are largely unknown or unavoidable. In perhaps 10% of cases, ingestion of NSAIDs, heavy alcohol binges and stress are clearly the culprit; this leaves 90% of patients not knowing what to expect, although some generalisations can be made, but these are too vague as to be clinically useful. However, because the clinical relapse is characterised by escalating inflammation, reaching a variable individual threshold when clinical symptoms become apparent, serial faecal calprotectin measurements offer the possibility of predicting the clinical relapse and initiating treatments at an asymptomatic stage. If successful, this has the potential to avoid hospitalisation with its attendant investigations and expenses.
The first study using calprotectin as a possible predictor for clinical relapse in patients with IBD was carried out at King’s College Hospital.3 Eighty one patients in clinical remission underwent the test and were closely followed up over the next year; just over 50% relapsed. The median faecal calprotectin (normal upper limit for the test kit was 10 mg/l) differed significantly between the relapse (median 123mg/l; 95% CI 98–213mg/l) and non-relapse (32mg/l; 95% CI 29–47mg/l) groups. Receiver operator curves showed that a fivefold increase in faecal calprotectin concentration gave the greatest sum of sensitivity and specificity. Faecal calprotectin above this had a sensitivity of 90% and specificity of 83% when patients with ulcerative colitis and Crohn’s disease were considered as a whole. These results have now been widely confirmed.
The clinical implications are clear.
Patients at minimal risk of clinical relapse of IBD may not need blank cover with 5-aminosalicylicilates or other drugs. Those at risk of relapse, as judged by high faecal calprotectin levels, may benefit from immediate treatment in order to avert the relapse with all its connotations and cost. Interestingly, selective white cell removal (leucocyte apheresis) in asymptomatic IBD patients with significantly raised faecal calprotectin levels reduced relapse rates from 68% to 27% over six months.
There are numerous examples of how faecal calprotectin can be used with a potential for subsequent routine use. Should patients with diverticulosis with raised faecal calprotectin be treated as though they had diverticulitis? Should patients with diabetic diarrhoea with raised faecal calprotectin be treated as though they have small bowel overgrowth? What about IBS and post-bariatric surgery patients with increased calprotectins? One of the most under-investigated areas of gastroenterology is the adverse effect of drugs on the small bowel. This ranges from metformin diarrhoea, which can come on at any time during diabetic treatment, to the vastly more serious and disabling gastrointestinal damage of chemotherapeutic drugs. Indeed, some chemotherapeutic treatments aim to give a dose according to gastrointestinal tolerability and the gut of patients undergoing bone marrow transplants remain without characterisation despite the fact that they have very severe gastrointestinal symptoms as a rule.
The consistency of findings between different research groups has given confidence in the calprotectin method. The test has the potential for widespread use in primary care, and in the case of patients with IBS, reducing the vast number of referrals to hospital-based gastroenterologists.9 Furthermore, there is an average of three years from when patients with IBD present to the GP to the time of diagnosis. The calprotectin method will pinpoint these patients with ease and facilitate diagnosis. The use of calprotectin in gastroenterology departments has the potential of substantial cost savings on expensive imaging and its careful use is already improving the prognosis of IBD.
- Tibble J et al. A simple method for assessing intestinal inflammation in Crohn’s disease. Gut 2000;47:506–13.
- Tibble JA et al. High prevalence of NSAID enteropathy as shown by a simple faecal test. Gut 1999;45:362–6.
- Tibble JA et al. Surrogate markers of intestinal inflammation are predictive of relapse in patients with inflammatory bowel disease. Gastroenterology 2000;119:15–22.
- Tibble JA et al. Use of surrogate markers of inflammation and Rome criteria to distinguish organic from nonorganic intestinal disease. Gastroenterology 2002;123:450–60.
- D’Haens G et al. Fecal calprotectin is a surrogate marker for endoscopic lesions in inflammatory bowel disease. Inflamm Bowel Dis 2012;18:2218–24.
- Nielsen HL et al. Evaluation of fecal calprotectin in Campylobacter concisus and Campylobacter jejuni/coli gastroenteritis. Scand J Gastroenterol 2013;48:633–5.
- Tibble J et al. Faecal calprotectin and faecal occult blood tests in the diagnosis of colorectal carcinoma and adenoma. Gut 2001;49:402–8.
- Henderson P et al. The diagnostic accuracy of fecal calprotectin during the investigation of suspected pediatric inflammatory bowel disease. Am J Gastroenterol 2012;107:941–9.
- Pavlidis P et al. Diagnostic accuracy and clinical application of faecal calprotectin in adult patients presenting with gastrointestinal symptoms in primary care. Scand J Gastroenterol 2013;48:1048–54.