Clinical Utility of Fecal Calprotectin Monitoring in Asymptomatic Patients with Inflammatory Bowel Disease: a systematic review and practical guide

Abstract

BACKGROUND & AIMS

In asymptomatic inflammatory bowel disease (IBD) patients, “monitoring” involves repeated testing aimed at early recognition of disease exacerbation. We aimed to determine the usefulness of repeated fecal calprotectin (FC) measurements to predict IBD relapses by a systematic literature review.

METHODS

An electronic search was performed in Medline, Embase and Cochrane from inception to April 2016. Inclusion criteria were prospective studies that followed patients with IBD in remission at baseline, and had at least 2 consecutive FC measurements with a test interval of 2 weeks to 6 months. Methodological assessment was based on the second Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) checklist.

RESULTS

A total of 1719 papers were identified; 193 were retrieved for full text review. Six studies met eligibility for inclusion. The time interval between FC tests varied between 1 to 3 months. Asymptomatic patients with IBD who had repeated FC measurements above the study’s cut-off level had a 53–83% probability of developing disease relapse within the next 2–3 months. Patients with repeated normal FC values had a 67–94% probability to remain in remission in the next 2–3 months. The ideal FC cut-off for monitoring could not be identified due to the limited number studies meeting inclusion criteria and heterogeneity between selected studies.

CONCLUSIONS

Two consecutively elevated FC values are highly associated with disease relapse, indicating a consideration to proactively optimize IBD therapy plans. More prospective data are necessary to assess whether FC monitoring improves health outcomes

INTRODUCTION

Inflammatory bowel disease (IBD), consisting of Crohn’s disease (CD) and ulcerative colitis (UC), is a chronic, relapsing and remitting disorder of the gastrointestinal tract. The ultimate goal in IBD is to restore disease remission as early as possible and to prevent disease progression and resistance to pharmacotherapies.¹ The concept of “monitoring” involves repeated testing aimed at early recognition of disease recurrence and timely adjustment of therapy plans.¹

The ideal monitoring test should be non-invasive, simple to conduct, and easily interpretable.² It should detect an imminent disease flare – often undetectable by symptom-based reporting alone – and makes provision for proactive treatment optimization. In Table 1, several frequently used targets for disease monitoring are compared and evaluated for their suitability as a monitoring test in IBD. While the gold standard for determining mucosal inflammation is endoscopy with histological confirmation,³ there is a need for clinically-useful biomarkers for monitoring purposes since it is unrealistic, costly, and potentially harmful to perform regular, invasive endoscopies.⁴ This rationale is particularly true in children affected by IBD^5–7 and patients with concomitant irritable bowel syndrome.^8,9

Table 1.

Markers of disease activity used in IBD patients.

	Validity (correlation with gold standard)	Responsiveness to changes in condition	Signal-to-noise ratio (ability to differentiate changes in condition from background variability)	Practicality
Endoscopy	Gold standard	Gold standard	Gold standard	Low Requires bowel preparation and in children general anaesthesia
Symptom-based clinical indices	Poor3,13,35–37	Moderate Affected by subjectivity6,7	Moderate Risk of false positive results (irritable bowel syndrome) and false negative results (dissimulation)9,38	High Easy to perform; non-invasive
C-reactive protein	Moderate3,12,13,35	Moderate Late position in disease progression pathway12,39,40	Moderate Risk of false positive results (acute infections and other inflammatory conditions) and false negative results (normal CRP despite active disease)39	High Quick result; but requires venepuncture
Fecal Calprotectin	Good12,29,38,41–43	Good Rises quickly in case of relapse; falls rapidly with successful treatment28	Moderate Risk of false positive results44,45	High Possible reluctance by patients for repeated stool collection.46

Calprotectin is a protein released by activated or damaged granulocytes, monocytes, macrophages and epithelial cells.¹⁰ It represents 60% of cytosolic protein in granulocytes and is resistant to metabolic degradation. Fecal calprotectin (FC) levels are related to neutrophil migration to the gastrointestinal tract.^10,11 FC is a more sensitive marker of active disease compared to the other frequently used surrogate markers (C-reactive protein (CRP)¹² and symptom-based clinical scoring systems,¹³ including Crohn’s Disease Activity Index (CDAI),¹⁴ Harvey Bradshaw Index,¹⁵ Pediatric CDAI,¹⁶ Simple Clinical Colitis Activity Index,¹⁷ and the Pediatric Ulcerative Colitis Activity Index(PUCAI).¹⁸ FC represents a practical monitoring test in IBD because testing can be done at home, and the protein is stable at room temperature for at least 3 days.¹⁹

A general construct for FC-based disease monitoring in patients with IBD is shown in Figure 1, which illustrates the four phases of disease monitoring.^1,20 Repeated FC measures are used to longitudinally track changes in a patient’s condition over time. In phase I, IBD is suspected, but neither endoscopically confirmed nor treated. In phase II, induction therapy is introduced to achieve disease control, resulting in patient response. Phase III begins with disease remission with continuation of maintenance therapy. The goal of monitoring in this phase is to detect deviations from the target range, indicating the start of phase IV. In phase IV, therapy is adjusted to re-establish disease control and bring FC levels back to the target range.

FIGURE 1. Conceptual model of FC monitoring in IBD patients.

Figure adapted from ‘Do Not Read Single Calprotectin Measurements in Isolation When Monitoring Your Patients with Inflammatory Bowel Disease’ by P.F. van Rheenen, Inflammatory bowel disease, 20:1416–7. Copyright 2014 by the Wolters Kluwer Health, Inc. Adapted with permission.

Given this background and clinical need for a standardized approach to non-invasive IBD monitoring, we performed a systematic review to evaluate whether FC monitoring could be used to detect imminent disease flares and sustained remission.

METHODS

Eligible studies were those that followed at least 10 patients with IBD in remission at baseline (monitoring phase III) and presented at least two consecutive FC measurements. We accepted FC test intervals between 2 weeks and 6 months. Studies that did not report the use of a FC cut-off (either predefined or based on receiver operating characteristic curves) were excluded from analysis.

Identification and selection of studies

We searched for studies published in Medline, Embase and the Cochrane Library. The search strategy for Medline was (“Leukocyte L1 Antigen Complex”[Mesh] OR “calprotectin”[tw] OR “calgranulin”[tw]) AND (“Inflammatory Bowel Diseases”[Mesh] OR “inflammatory bowel disease”[tw] OR “inflammatory bowel diseases”[tw] OR “IBD”[tw] OR “Crohn”[tw] OR “Colitis”[tw]). For Embase we used (“calgranulin”/exp OR “calprotectin”/exp) AND (“enteritis”/exp OR “inflammatory bowel disease”/exp OR “inflammatory bowel diseases”/exp OR “ibd” OR “crohn” OR “colitis”/exp). We restricted our search to studies published in English only. Duplicate articles were manually deleted using RefWorks. For further relevant studies, we checked the reference lists of identified papers. The first selection of studies was carried out by one reviewer (AH) on the basis of title and abstract. The full paper of each potentially eligible study was then obtained. Two authors (AH and PvR) independently assessed full manuscripts against the predefined inclusion criteria. Any disagreements were resolved by discussion, and consensus was reached with the third author (KTP).

Data extraction and management

The following characteristics were extracted from each selected study: name of first author, year of publication, country of origin, journal, study design criteria (prospective vs. retrospective design), sample size (the number of patients in follow-up), baseline characteristics (type of IBD, age group), FC test characteristics (including cut-offs tested), reference standard (endoscopy), other markers of disease activity used (including symptom-based clinical indices and CRP), prevalence of disease flares and the number of true positives, true negatives, false positives, false negatives.

Pooling of data was greatly jeopardized due to heterogeneity between studies and was therefore not undertaken.

Assessment of risk of bias and applicability concerns

Study quality was assessed using the QUADAS-2 (QUality Assessment of studies of Diagnostic Accuracy included in Systematic reviews) checklist.²¹ In QUADAS four key domains are rated for risk of bias and concerns regarding applicability to the review questions. The signalling questions in each domain were specifically tailored to our review questions (Supplementary Table 1). We did not calculate summary scores because their interpretation is problematic and potentially misleading.²²

RESULTS

This review includes results of electronic searches up to 21 April 2016. A total of 1719 papers were identified, of which 193 were retrieved for full text review. Of these, 187 were excluded for not meeting the eligibility criteria. Six papers were included in the final analysis (Figure 2).

FIGURE 2. Flow diagram systematic literature search.

Reasons for exclusion at last stage (*):

- Serial measurements of FC not reported (n=69)

- Congress abstract (n=53)

- Patients had active disease at baseline (n=29)

- FC test interval out of desired range (<2 weeks or >6 months) (n=14)

- Narrative review, Editorial, Letter to editor, or Comment (n=7).

- FC test results within 6 months before relapse not reported (n=7)

- FC cut-point not reported (n=3)

- Language other than English (n=3)

- Less than 10 participants (n=2)

Study characteristics

Study characteristics of included studies are presented in Table 2. All studies were published in the most recent 3 years, and all except one were from European countries. Sample size varied between 49 and 181 patients. All except one study included adult patients only.²³ The mean proportion of patients experiencing a disease flare during the observation period was 33.3% (184 of 552; range 27 to 50%), and the total observation period was 10 to 18 months. All studies included patients with UC of which one followed patients with disease exclusively confined to the rectum.²⁴ Two studies also included patients with CD.^23,25 The time interval between consecutive FC tests varied between one and three months. One study compared control patients assigned to usual care with patients exposed to a FC-guided dose-escalation scheme with oral 5-aminosalicylates.²⁶ For the sake of clarity we excluded the intervention group from our analysis, since the number of relapses in the intervention group was directly influenced by the therapeutic intervention.

TABLE 2.

Study characteristics of selected studies

Study	N of patients in follow-up	Age group	Study aim (Prospective if not otherwise specified)	Type of IBD; remission at baseline	Proportion of patients with relapse	Median duration of follow-up (in months)	Frequency of diagnostic testing (scoring method)
							Fecal calprotectin	Endoscopy	Clinical Activity score	CRP
Dabritz 201323 Germany	181	AC	Monitoring disease activity	UC (120); CD (61)	34%	10	Every 3 months or when suspicion of relapse		Every 3 months or when suspicion of relapse (P)CDAI, (P)UCAI	Every 3 months or when suspicion of relapse
De Vos 201328 Belgium, Norway	87	A	Monitoring disease activity	UC (87)	33%	12 or relapse	Every month	Baseline, week 52 (Sigmoidoscopy, Mayo endoscopic subscore)	Every 2 months or when suspicion of relapse (Partial Mayo score)	Every 2 months or when suspicion of relapse
Jauregui-Amezaga 201427 Spain	64	A	Evaluating accuracy of HR-rectosigmoidoscopy	UC (64)	27%	12 or relapse	Every 3 months	Baseline, 12 months or relapse (HR- rectosigmoidoscopy)	Every 3 months (Mayo score)	Every 3 months
Lasson 201526 Sweden	91	A	RCT comparing FC-based pharmacological intervention and usual care	UC (91), control group (40), intervention group (51)	Intervention group 35%; usual care 50%; overall 42%	18	Every month	Baseline (Sigmoidoscopy)	Baseline (Mayo score)
Molander 201525Finland	49	A	Monitoring and predicting disease activity after stopping anti-TNF therapy	UC (28); CD (16); IBD-U (5)	31%	12	0,1,2,3,4,5,6,8,10,12 months or when suspicion of relapse	0,4,12 months or when suspicion of relapse (Ileocolonoscopy SES-CD or Mayo endoscopic subscore (UC))	0,1,2,3,4,5,6,8,10,12 months or when suspicion of relapse (HBI (CD) or partial Mayo (UC))	0,1,2,3,4,5,6,8,10,12 months or when suspicion of relapse
Yamamoto 201524 Japan	80	A	Monitoring disease activity	UC-proctitis: (80)	30%	10	Every 2 months	Baseline and when suspicion of relapse (Endoscopy, UC-DAI score)	Every 2 months (UC-DAI score, PGA)	Every 2 months
Total	552				33.3%

Abbreviations: A = adults; C = children; CD = Crohn’s Disease; HBI = Harvey Bradshaw Index; IBD = inflammatory bowel disease; IBD-U = IBD-unclassified; N = number of participants; (P)CDAI = (Pediatric) Crohn’s Disease Activity Index; PGA = Physicians Global Assessment; (P)UCAI = (Pediatric) Ulcerative Colitis Activity Index; SES-CD = Simple Endoscopic Score for Crohn’s disease; UC = ulcerative colitis; UC-DAI = Ulcerative Colitis Disease Activity Index.

Methodological quality of included studies

The methodological quality of the included studies is summarized in Table 3. All studies used a prospective design, enrolled patients with IBD in remission, used a commercially available FC assay, and tested FC during the initial remission period and periodically thereafter. One study used only clinical activity scores as reference standard instead of endoscopic evaluation.²³ In half of the studies endoscopy was scheduled according to the protocol when relapse was suspected.^24,25,27 Differential verification was evident in three studies.^25,26,28 Substantial differences between studies were observed in clinical and endoscopic definitions of relapse and predefined FC cut-off levels.

TABLE 3.

QUADAS-2 checklist

Study	Risk of bias				Applicability concerns
	Patient selection	Index test	Reference standard	Flow and timing	Patient selection	Index test	Reference standard
	Dabritz 201323
De Vos 201328
Jauregui-Amazega 201427
Lasson 201526
Molander 201525
Yamamoto 201524

= low risk of bias; = high risk of bias; = unclear risk of bias

Findings

Prognostic value of repeated FC measurements for relapse and sustained remission

All patients included in the final analysis collected the first feces sample while in remission. Most individual studies showed that asymptomatic patients with FC levels moving out of the normal range on the next measurement had higher risk of relapse within the next 2 to 3 months. When FC was elevated the probability of relapse increased to 53–83%, as is shown in Table 4.^24–28 Consecutive normal FC values were associated with reduced risk of relapse, with 67–94% probability of remission in the next 2 to 3 months.

TABLE 4.

Characteristics of fecal calprotectin monitoring studies

Study	FC assay	Upper limit of normal range (in μg/g)	Basis of relapse diagnosis	Pretest probability of relapse	Post-test probability of relapse		Time between drift out of normal range to relapse	N per 100 patients
					when upward trend in FC out of normal range (95% CI)	when consecutive values in normal range (95% CI)		True Positives	True Negatives	False Positives	False Negatives
Dabritz 201323	Immunodiagnostic	15	C	34%	63% (55 to 71%)	12% (8 to 19%)	2–3 months	27	51	15	7
De Vos 201328	PhiCal	300*	C&E	33%	83% (61 to 94%)	20% (15 to 27%)	3 months	17	63	4	16
Jauregui-Amazega 201427	Cerba internacional	250	E	27%	53% (33 to 73%)	18% (12 to 26%)	3 months	13	62	11	14
Lasson 201526 **	Buhlmann	300	C	50%	57% (47 to 67%)	33% (15 to 58%)	Unknown	40	20	30	10
Molander 201525	Calpro	200	E	31%	57% (36 to 76%)	20% (12 to 30%)	2–4 months	17	57	12	14
Yamamoto 201524	Canton	55	E	30%	66% (52 to 77%)	6% (2 to 16%)	2 months	26	56	14	4

Abbreviations: CI: confidence interval; C: relapse defined as clinical relapse; E: relapse defined as endoscopic relapse; C&E: relapse defined as both clinical relapse or endoscopic relapse.

^*FC value above cut-off in two consecutive months.

^**Only control group included in this table.

One study investigated the prognostic value of ≥2 consecutive measurements above the upper limit of normal,²⁸ while the others focussed on an upward trend of FC between two measurements.^23–27 As can be seen in Table 5, the former strategy resulted in the highest probability of relapse.

TABLE 5.

Implications of fecal calprotectin test results

Outcomes	Consequences	Importance*
True positives	Interpretation: Patient has active disease despite being symptom-free Presumed patient outcome: May benefit from shorter delay and potential early adjustment of therapy (intensify/switch/add)	CRITICAL
True negatives	Interpretation: Patient is in remission Presumed patient outcome: Benefit from reassurance	CRITICAL
False positives	Interpretation: Patient is in remission, FC elevated Presumed patient outcome: Detriment from exposure to overtreatment	CRITICAL
False negatives	Interpretation: Patient has active disease, but it is not (yet) recognised Presumed patient outcome: Detriment from delayed diagnosis and delayed adjustment of therapy False reassurance leading to ignoring symptoms	CRITICAL
Inconclusive results	Interpretation: Not sure whether this increase in FC is clinically relevant Presumed patient outcome: Detriment from increased anxiety by uncertainty until next FC test result May benefit from avoidance of overtreatment	CRITICAL
Complications of test	May be perceived as unsanitary	NOT IMPORTANT
Resource utilization (cost)	Increases cost for ambulant diagnostic testing; however, endoscopy has much greater resource implications. FC-based home monitoring may reduce cost for out-patient health checks	IMPORTANT

^*GRADE recommends classifying each outcome as either “critical for decision making”, “important but not critical for decision making”, or “not-important”.

Optimal FC cut-off for monitoring disease activity

Probabilities of relapse and remission varied between studies, partly because different FC cut-offs were used. Variation in FC cut-offs could not explain all the difference. Patient variation, study design and type of FC assay may also have contributed to the heterogeneity of the test accuracy. Because of the limited number of studies included in this systematic review, we were not able to derive the ideal cut-off point.

DISCUSSION

In this systematic review, we evaluated the utility of FC monitoring to detect imminent flares in asymptomatic patients with IBD. We identified only six studies meeting our inclusion criteria. Data collection was done prospectively in consecutive series of mostly UC patients with quiescent disease at baseline. We found that there was poor consistency of reference standard use and definition of relapse between the studies. Two consecutively elevated FC levels appeared to be the best predictor for relapse, but this was systematically investigated in only one study.²⁸ An upward trend of FC out of the normal range was also prognostic for relapse, albeit with a lower probability of relapse.

Comparison with other reviews

We report the first systematic review that investigates the prognostic value of repeated FC measurements in asymptomatic patients with IBD. To date, there have been two meta-analyses of the diagnostic accuracy of a single FC measurement in almost exclusively symptomatic patients with previously diagnosed UC or CD.^12,29 In these circumstances, symptom-based clinical indices and derangements in serological markers of inflammation would likely lead clinicians to intensify medical therapy. Inclusion of these studies may cause overestimation of the prognostic value of calprotectin relative to the practical situation, where a monitoring test is necessary to discriminate between those who have preclinical relapse and those with quiescent IBD. We moved away from single FC measurements that are read in isolation when relapse is suspected, and focused on repeated FC measurements in asymptomatic patients to predict relapse.

Based on our review, we found that FC levels start rising 2 to 3 month before a relapse becomes apparent, and therefore support the biological implausibility that a single FC measurement at baseline can predict the clinical course over a 12 months period, as was suggested in a meta-analysis by Mao et al.³⁰

Cut-off levels

Furthermore, we were not able to identify the best FC cut-off for monitoring purposes. Currently, there is no consensus among IBD experts about the range of FC associated with mucosal healing, indicating a need for prospective and randomized studies comparing monitoring strategies that vary in thresholds.

Clinical Implications

Table 5 elaborates on the specific outcomes when FC monitoring strategy leads to effective adjustments in IBD therapy from a patients’ perspective. The underlying assumption here is that FC monitoring serves to improve patient-centered outcomes, representing a proactive approach to detecting indolent disease activity. Of note, when adopting FC monitoring, key questions most relevant to decision making are whether the numbers of false negatives (missed cases with relapse) and false positives (cases without disease activity who may receive treatment intensification) are acceptable within the new monitoring paradigm. Emerging evidence suggest that FC monitoring has the potential to result in less missed cases of asymptomatic IBD patients with on-going mucosal-level inflammation. In particular, IBD patients who underreport symptoms and pediatric patients requiring anesthesia for each endoscopic evaluation are two subset of patients who may benefit from FC monitoring. From a patient perspective, bowel preparation for colonoscopy, repeated anaesthesia, and incurring indirect costs are practical and important considerations in favor of FC monitoring. Additionally, FC monitoring may serve as a feedback tool for better patient engagement, facilitating self-management strategies of their chronic condition.

Although there is no consensus on the optimal frequency of calprotectin retesting and cut-offs for treatment intensification, the authors of this paper routinely monitor children with IBD using an enzyme-linked immunosorbent assay (ELISA) allowing quantification. A practical cut-off range could be as follows: levels below 250 μg/g as indicative for disease remission (green), levels above 500 μg/g as indicative for disease flare (red), while levels between 250 and 500 μg/g indicating need for more frequent calprotectin monitoring (yellow), as shown in Figure 1. This “traffic light” is currently being evaluated in a prospective multicenter telemonitoring program.³¹ Future studies are needed to determine whether pre-emptive treatment intensification based on elevated FC levels will lead to long-term better patient outcomes, including reduction of hospitalizations, disability-associated costs and loss of productivity. The first prospective trials with mesalamine dose intensification^26,32,33 and infliximab dose interval adjustment³⁴ have already been performed with promising results.

Methodological limitations of the review

Although the methodology to conduct a systematic review and meta-analysis of diagnostic research is developed to a certain extent, at least for dichotomised tests, the systematic evaluation of a monitoring test is not bound to consensus guidelines. Although the papers we selected had to meet high methodological standards, we acknowledge several limitations. Significant heterogeneity in disease spectrum, study endpoints, FC cut-off levels, and quality of reporting are potentially confounding factors that may affect interpretation of the data and conclusions. Also, we restricted our search to studies published in English only, leading to potential bias.

Conclusion

This systematic review shows that the relapsing and remitting nature of IBD becomes less unpredictable with proactive FC monitoring in clinical practice, allowing early recognition of relapse prior to overt symptoms (or symptom reporting). While FC monitoring may represent a more proactive strategy for treatment modifications in a treat-to-target approach, more robust data are necessary to determine whether it will improve decision-making and patient-centered outcomes.

Abbreviations

CD

Crohns disease

FC

Fecal calprotectin

IBD

Inflammatory bowel disease

UC

Ulcerative Colitis

QUADAS

QUality Assessment of studies of Diagnostic Accuracy included in Systematic reviews