Inflammatory Bowel Diseases (IBD) comprise ulcerative colitis (UC) and Crohn’s disease (CD). Management of IBD requires assessment of disease activity, severity, extent and complications. Here, we describe the signal behavior of both CD and UC in 68Gallium- fibroblast activation protein inhibitor-based radiopharmaceuticals-46-positron emission tomography (68Ga-FAPI-46-PET) and evaluate the potential of 68Ga-FAPI-46-PET for activity assessment in IBD. This analysis includes data of 43 IBD patients and 43 control patients examined by 68Ga-FAPI-46-PET/computed tomography (CT). Disease activity of IBD patients was assessed by colonoscopy. FAPI-positive gastrointestinal tract (GIT)-findings and healthy appearing GI structures were contoured. Non-IBD related FAPI-positive GIT-findings were ruled out by interdisciplinary consensus. Static and dynamic PET-parameters of FAPI-positive IBD lesions and healthy appearing GI structures were extracted and PET signalling was analyzed with respect to IBD subtype and disease activity. We examined 20 CD patients and 23 UC patients (29 with active, 14 with inactive disease). FAPI-uptake in most healthy appearing GI structures of IBD patients was significantly increased compared to controls. Of 80 FAPI-positive GIT-findings, 14 were ruled out as non-IBD related and 66 FAPI-positive IBD lesions were analyzed. We observed equally high lesional FAPI-uptake in CD and UC. All patients with active disease showed at least one intensively FAPI-positive IBD lesion, while only 4/14 patients with inactive disease showed any FAPI-positive IBD lesion. Lesional and patientwise FAPI-uptake was significantly higher in active than in inactive disease. FAPI-positive IBD lesions showed a characteristic kinetic behaviour with two types of uptake patterns – one showing a continuous increase and the other an early peak followed by a plateau. 68Ga-FAPI-46-PET/CT appears promising for assessing disease activity in terms of fibroblast activation in both CD and UC.

BACKGROUND:Real-world evidence studies of ustekinumab (UST) in ulcerative colitis (UC) are needed because randomized controlled trials do not represent unselected patient populations in everyday clinical practice. Patients with UC were recruited when starting biologic therapy for the first time or switching to a new biologic therapy. This study assessed the effectiveness of maintenance therapy with UST in comparison to anti-TNF or vedolizumab (VDZ) at 12 months. METHODS:Between 2020 and 2022, 507 UC patients starting biologic therapy for the first time or switching to a new biologic therapy were enrolled at 34 inflammatory bowel disease (IBD)-specialized centers in Germany. After excluding patients receiving other biologics or small molecules, as well as those with stomas or missing outcomes, the final sample consisted of 476 patients. The outcomes were clinical response, clinical remission (CR), and steroid-free remission. Propensity score (PS) adjustment with inverse probability of treatment weighting was used to reduce the effect of confounding due to physician selection of therapy. RESULTS:A total of 476 patients with UC were included in the analysis (UST: 147, anti-TNF: 168, VDZ: 161). Treatment persistence over 12 months differed significantly (P < .001) between UST (93.9%), VDZ (87.0%), and anti-TNF (75.0%). The PS-weighted effectiveness of UST in the mITT analysis at month 12 was not significantly different from anti-TNF or VDZ (CR: UST 26.9%, anti-TNF 34.7%, VDZ 40.9%; P = .063). CONCLUSIONS:In the prospective RUN-UC study with PS-weighted groups, UST showed higher treatment persistence but no significant difference in maintenance effectiveness compared to anti-TNF or VDZ in UC.

Ziel/Aim: Inflammatory Bowel Disease (IBD), comprise a complex spectrum of chronic inflammatory conditions of the gastrointestinal tract (GIT) including ulcerative colitis (UC) and Crohn´s disease (CD). Management and monitoring of IBD necessitate the use of various diagnostic modalities including enteroscopy and cross-sectional imaging to assess disease activity, extent, and complications. Given the role of fibroblast activation and tissue remodeling in the pathophysiology of IBD, we aimed to explore the potential of the application of 68Ga-FAPI-PET in the context of IBD.

Abstract Background Treatment options for patients with ulcerative colitis have increased considerably in recent years. Here, we present the 6-month results on clinical effectiveness and psycho-social outcomes of the ongoing FilgoColitis study in patients with ulcerative colitis (UC) starting new treatment with filgotinib (FIL) in a real-world setting. Methods FilgoColitis is a prospective, multicentre, non-interventional, 24-month observational study in patients with active UC and newly introduced FIL therapy. Disease activity (clinical response: reduction of pMayo by ≥3 points from baseline to month 6 and a reduction of at least 30% or reaching remission at month 6; clinical remission (CR): pMayo ≤ 1 plus a bleeding subscore=0; steroid-free remission: CR and no systemic use of steroids or oral budesonide), quality of life (QoL) (sIBDQ and EQ-5D), and fatigue level (FACIT-F) will be analyzed. In a subgroup, the daily step count was recorded using the SensMotion® thigh accelerometer for at least 3 days after each visit (n=21). Results 202 patients were enrolled in the study. After excluding missing outcomes, 164 patients were available for the 6-month analysis. Of these, 61.0% were male, and the median time since diagnosis was 8.0 years. Before treatment with FIL, 85.4% of patients had received biologic or small molecule therapies, and 57.3% had used immunosuppressants. Treatment persistence at month 6 was 87.2% (Fig. 1). After 6 months of treatment with FIL, the clinical response and remission rate were 59.2% and 41.7%, respectively (mITT (switchers=outcome failures), Table 1). There was no significant difference in clinical remission between biologic-naïve and biologic-experienced patients (41.7% vs 41.4%). Looking at week-10 responders only, the response rate at month 6 was 85.0%, and the remission rate was 58.8%. QoL improved significantly, with median EQ-VAS scores increasing from 64 to 80 at month 6 (p<0.001), and sIBDQ scores improving from 42.0 to 56.0 (p<0.001). Fatigue scores improved significantly from baseline to month 6 of FIL therapy (FACIT-F score part I: 8.0 vs 5.0, p<0.001). In patients who were in remission at month 6, the daily number of steps measured was higher than in patients who were not in remission (9918 (4861-11048) vs 5959 (4747-6323)). The steps measured during the night also differed between these two groups: 196 (142-559) vs 293 (164-479). This was consistent with asking the patients if they had nocturnal stools (0% vs 42.9%). Conclusion In this real-world study, FIL showed a clinical response rate of 59% and a clinical remission rate of 42% at month 6 in patients with active UC, demonstrating a further improvement compared to the induction phase. QoL was also significantly improved.

Schlüsselwörter chronisch-entzündliche Darmerkrankungen - CED - Diagnose - Therapie - Remission - Remissionserhaltung

Abstract Background Observational real-world evidence (RWE) studies on the effectiveness and safety of ustekinumab (UST) in ulcerative colitis (UC) are required in addition to RCTs, which are usually confined to selected patients and thus may not represent distinct treatment patterns and everyday clinical practice. For this reason, the prospective, controlled, propensity score (PS)-adjusted RUN-UC study was conducted in UC patients starting a newly initiated biologics therapy with a follow-up period of 3 years. The aim of the present analysis was to investigate the induction phase effectiveness of UST vs anti-TNF vs vedolizumab (VEDO) in UC in terms of clinical and steroid-free remission. Methods Between 2020-2022, 507 UC patients starting a new therapy with UST or other biologics were enrolled in 34 IBD-experienced centres across Germany. After exclusion of small molecules and missing outcomes, the final sample consisted of 317 patients. Response modified (reduction of partial Mayo score (pMayo) by ≥ 3 points from baseline to week-16 and a reduction of at least 30% or reaching remission at week-16), clinical remission (pMayo ≤ 1 plus a bleeding subscore=0), and steroid-free remission (pMayo ≤ 1, bleeding subscore=0 and no systemic use of steroids or oral budesonide during the last 8 weeks) were considered as outcomes. To reduce the effect of confounders, PS adjustment with inverse probability of treatment weighting (IPTW) was implemented. A weighted logistic regression was used, and the results were reported as odds ratio (OR) and 95% confidence interval (CI). Health-related quality of life was assessed by using the self-reported visual analogue scale (EQ-VAS) of the EQ-5D. Changes in EQ-VAS from baseline to week-16 were assessed with a linear model. Results 101 UST (bio-naïve: 6), 106 anti-TNF (ADA: 24.5%, IFX: 65.1%, GOL: 10.4%) (bio-naïve: 70) and 110 VEDO (bio-naïve: 73) UC-patients were included. PS adjustment removed systematic differences between the three groups (UST/anti-TNF/VEDO: 44.9/43.8/48.1% males, 6.7/9.9/5.5% smokers, 7.9/12.5/9.3% EIM). The effectiveness of UST in terms of response, clinical and steroid-free remission was comparable to that of anti-TNF and VEDO at week 16 (Tab. 1). We observed a significant increase in EQ-VAS within all three groups (Tab. 2). The increase in the UST group was significantly higher than in the VEDO group and numerically higher than in the anti-TNF group. Conclusion In this prospective RUN-UC study, with propensity score weighted groups, UST showed similar induction phase effectiveness in comparison with anti-TNF and VEDO. Quality of life was significantly improved in the UST group vs VEDO and was numerically higher than anti-TNF after the induction phase.

Abstract Background Observational real-world evidence (RWE) studies on the effectiveness of ustekinumab (UST) in ulcerative colitis (UC) are needed in addition to RCTs, which may not represent everyday clinical practice. For this reason, the prospective, controlled, propensity score (PS)-adjusted RUN-UC study was conducted on UC patients starting a new biologic therapy with a follow-up period of up to 3 years. The aim of the present analysis was to evaluate the 1-year maintenance therapy effectiveness of UST vs. anti-TNF or vedolizumab (VDZ). Methods Between 2020-2022, 507 UC patients starting a new therapy with UST or other biologics were enrolled in 34 IBD-experienced centres in Germany. After the exclusion of patients with a stoma, small molecules and missing outcomes, the final sample consisted of 476 patients. Response modified (reduction in partial Mayo score (pMayo) by ≥3 points from baseline to month 12 and a reduction of at least 30% or achievement of remission at month 12), clinical remission (CR) (pMayo ≤ 1 plus a bleeding subscore=0) and steroid-free remission (pMayo ≤ 1, bleeding subscore=0 and no systemic use of steroids or oral budesonide use in the previous 8 weeks) were considered as outcomes. To reduce the effect of confounders, PS adjustment with inverse probability of treatment weighting (IPTW) was implemented. Health-related QoL was assessed by using the visual analogue scale (EQ-VAS) of the EQ-5D. Results A total of 476 UC-patients [147 UST (bio-naïve: 12), 168 anti-TNF (ADA: 32.7%, IFX: 59.5%, GOL: 7.7%) (bio-naïve: 114) and 161 VDZ (bio-naïve: 105)] were included in the analysis. The PS-adjustment eliminated systemic differences in the baseline parameters (UST/anti-TNF/VEDO: 42.2/47.0/50.3% males, 25.2/25.0/19.9% EIMs), in particular, the "bio-experienced" characteristic was also equalised, between the groups. Treatment persistence over 12 months was different between UST (93.9%), VDZ (87.0%) and anti-TNF (75.0%) (Fig. 1). The PS-weighted effectiveness of UST (mITT analysis) in terms of response, clinical and steroid-free remission at month 12 (Tab. 1) was comparable to that of anti-TNF and VDZ, as was also the case without PS-weighting (CR: UST 33.1%, anti-TNF 38.5%, VDZ 38.1%). Patients of all treatment groups showed significant improvements in QoL measured as the EQ-VAS after 12 months of treatment. Conclusion In this prospective RUN-UC study with PS-weighted groups, UST showed similar maintenance effectiveness compared to established biologics in UC (anti-TNF and VDZ) with a relatively higher treatment persistence of UST, probably serving as a proxy for effectiveness, suggesting that additional criteria, such as safety and patients´ profile, may play an important role in the selection of biologics.

BACKGROUND The aim of this observational, real-world evidence, modified intention-to-treat (mITT) study based on prospectively collected data from the VEDOIBD registry was to compare the effectiveness of vedolizumab (VEDO) vs antitumor necrosis factor (anti-TNF) in biologic-naïve Crohn's disease (CD) patients. METHODS Between 2017 and 2020, 557 CD patients starting therapy with VEDO or anti-TNF were consecutively enrolled in 45 IBD centers across Germany. Per study protocol, the analysis excluded biologic-experienced patients and those with a missing Harvey-Bradshaw Index score, resulting in a final sample of 327 biologic-naïve CD patients. Clinical remission was measured using the Harvey-Bradshaw Index at the end of induction therapy and after 1 and 2 years. Switching to a different therapy was considered an outcome failure. Propensity score adjustment with inverse probability of treatment weighting was used to correct for confounding. RESULTS The effectiveness of both VEDO (n = 86) and anti-TNF (n = 241) was remarkably high for induction treatment, but VEDO performed significantly less well than anti-TNF (clinical remission: 56.3% vs 73.9%, P < .05). In contrast, clinical remission after 2 years was significantly better for VEDO compared with anti-TNF (74.2% vs 44.7%; P < .05; odds ratio, 0.45; 95% CI, 0.22-0.94). Remarkably, only 17% of patients switched from VEDO to another biologic vs 44% who received anti-TNF. CONCLUSIONS The results of this prospective, 2-year, real-world evidence study suggest that the choice of VEDO led to higher remission rates after 2 years compared with anti-TNF. This could support the role of VEDO as a first-line biologic therapy in CD.

Abstract Background To gain insight into vedolizumab (VEDO) use as a first-line biologic in Crohn′s disease (CD), this comparative, two-arm prospective real-world-evidence (RWE) study with propensity score (PS) adjustment aimed to assess, within the maintenance phase, the 2-year comparative effectiveness and persistence of VEDO vs anti-TNF therapy in biologic-naïve CD patients. Methods Between 2017-2020, 1200 consecutively enrolled biologic-naïve and biologic-experienced patients with ulcerative colitis (UC) and CD were prospectively included in the VEDOIBD study from 45 IBD-experienced centres across Germany. 260 biologic-naïve CD patients starting a new therapy with VEDO or anti-TNF were included in this RWE comparison of VEDO vs anti-TNF. The Kaplan-Meier curve was used to summarize the treatment persistence from the start of therapy through week-104. The primary outcome was two-year clinical remission (HBI ≤ 4). Patients were analysed on a modified intent-to-treat basis (mITT; switchers considered as outcome failure). To reduce the effect of confounders, PS adjustment with inverse probability of treatment weighting (IPTW) was implemented. A weighted logistic regression was used to evaluate the effectiveness. The results were reported as odds ratio (OR) and 95% confidence interval (CI). Results 63 VEDO and 197 anti-TNF (ADA: 58.4%, IFX: 41.6%) biologic-naïve CD-patients were evaluated. Two years after treatment initiation approximately 83% of VEDO patients were still in continuous treatment vs only 56% of anti-TNF patients (Fig. 1). In the mITT analysis (Fig. 2), there was a significantly higher clinical remission rate with VEDO when compared to anti-TNF after two years (VEDO: 64.2% vs anti-TNF: 44.7%), and a higher steroid-free remission (VEDO: 62.5% vs anti-TNF: 41.6%). Both differences were statistically significant (p<0.05). Additionally (Fig. 3), using IPTW to examine the two-year maintenance effectiveness in week-14 induction phase responders, there was a significantly better response in terms of clinical remission for VEDO (88.6%) compared to anti-TNF (45.8%) (p=0.0001) and in steroid-free remission of 86.8% for VEDO compared to 44.1% for anti-TNF (p<0.001). Conclusion Compared to previous RCTs, this prospective two-year RWE study comparing VEDO with anti-TNF showed that, in biologic-naïve CD patients, remission rates at two years with VEDO were remarkably higher than with anti-TNF. Given the favourable side effect profile of VEDO, these findings may aid physicians’ decision-making on the choice of VEDO as a first-line biologic for CD.

SummaryBackgroundThis observational real‐world evidence (RWE) study is based on prospectively collected data from the VEDOIBDregistry study.AimTo compare the effectiveness of vedolizumab and anti‐TNF agents in biologic‐naïve patients with ulcerative colitis (UC) at the end of induction and during maintenance treatment.MethodsBetween 2017 and 2020, we enrolled 512 patients with UC starting therapy with vedolizumab or an anti‐TNF agent in 45 IBD centres across Germany. We excluded biologic‐experienced patients and those with missing partial Mayo (pMayo) outcomes; this resulted in a final sample of 314 (182 on vedolizumab and 132 on an anti‐TNF agent). The primary outcome was clinical remission measured using pMayo score; any switch to a different biologic agent was considered an outcome failure (modified ITT analysis). We used propensity score adjustment with inverse probability of treatment weighting to correct for confounding.ResultsDuring induction therapy, clinical remission was relatively low and similar in vedolizumab‐ and anti‐TNF‐treated patients (23% vs. 30.4%,p = 0.204). However, clinical remission rates after two years were significantly higher for vedolizumab‐treated patients than those treated with an anti‐TNF agent (43.2% vs. 25.8%,p < 0.011). Among patients treated with vedolzumab, 29% switched to other biologics, versus 54% who had received an anti‐TNF agent.ConclusionAfter two years of treatment, vedolizumab resulted in higher remission rates than anti‐TNF agents.

Abstract Background In this two-arm prospective real-world-evidence (RWE) study with propensity score adjustment, we aimed to analyse the persistence of biologic therapy in biologic-naïve ulcerative colitis (UC) patients and to compare the 2-year effectiveness of vedolizumab (VEDO) and anti-TNF. Methods Between 2017 and 2020, 1200 consecutively enrolled biologic-naïve and biologic-experienced patients with UC and CD (Crohn’s disease) were prospectively included in the VEDOIBD study from 45 IBD-experienced centres across Germany. After the exclusion of biologic-experienced patients, CD, and missing outcomes, the final sample consisted of 314 biologic-naïve UC patients with 2-year follow-up data. In this mITT analysis switching was considered as outcome failure, and clinical remission and (steroid-free) remission rates (pMayo ≤1 plus a bleeding subscore=0 - and no systemic use of steroids or oral budesonide at two years) at two years were predefined as outcomes. To reduce the effect of confounders, propensity score (PS) adjustment with inverse probability of treatment weighting (IPTW) was implemented. A weighted logistic regression was used, and the results were reported as odds ratio (OR) and 95% confidence interval (CI). Results The two-year maintenance phase effectiveness of 182 VEDO and 132 anti-TNF (ADA: 25.8%; IFX: 58.3%; GOL 15.9%) biologic-naïve UC patients were analysed in this prospective RWE-comparison of VEDO vs anti-TNF. Significantly more patients switched to another biologic in the anti-TNF group when compared to the VEDO group up to 2 years (54% vs 29%; p<0.0001) (Fig. 1). In the mITT analysis after 2 years a statistically significant higher clinical remission rate of 43.2% was found for VEDO vs 25.8% for anti-TNF (OR 95% 2.18 (1.19-3.99), p=0.011) (Fig. 2). Considering the two-year effectiveness of ADA and IFX the response rates of VEDO were numerically higher than those of ADA (45.2% vs 37.9%) but not statistically significant. In contrast, for VEDO versus IFX, there was a clear difference in favour of VEDO that resulted in a clinical remission rate of 43.1% versus 16.5% for IFX (p=0.0003). Conclusion As shown previously, in the induction phase, there is comparable effectiveness for VEDO and anti-TNF, although the remission rates are relatively low and similar to the range reported in RCTs. Over one year, the effectiveness tends to improve in favour of VEDO, potentially due to better treatment persistence. After two years, the clinical remission rate in the VEDO group is statistically significantly higher than in the anti-TNF group. The higher treatment persistence of VEDO vs anti-TNF and the higher effectiveness may suggest VEDO as a first-line biologics therapy option in UC patients.

Abstract Background Since April 2020, vedolizumab (VEDO) has been available for use in IBD in intravenous (iv) and subcutaneous (sc) formulations. Due to limited data on real-world use and effectiveness, the objectives of this real-world evidence (RWE), observational, prospective study are to observe (1) the time point of conversion to VEDO sc, (2) the 6-month remission rate with VEDO sc. using data from the VEDOIBD study. Methods Between 2017-2020, 1200 consecutively enrolled patients with ulcerative colitis (UC) and Crohn’s disease (CD) were prospectively included in the VEDOIBD study from 45 IBD-experienced centers across Germany. Additionally, 74 VEDO-naïve patients were included with the goal of conversion to VEDO sc after an iv-induction period with VEDO (VEDO iv week 0, 2, 6). Effectiveness was measured by clinical remission (HBI ≤ 4) at month 6. Results A total of 180 IBD patients with a running VEDO iv therapy were converted to VEDO sc during the entire study, with at least one 6-month visit from 119 patients (UC: n=67; CD: n=52). Characteristics are shown in Table 1. 87 IBD patients (73.1%) were still receiving VEDO sc after 6 months. 32 IBD patients (26.9%) stopped VEDO sc therapy within the first 6 months. The majority of patients returned to treatment with VEDO iv (37.9%) and the others switched to other biologics: 24.1% ustekinumab, 34.5% anti-TNF (Figure 1). At the time of conversion to sc, 92 patients (77.3%) were in remission (UC: 75%; CD: 84.6%). Of those, 88% remained in remission at 6 months (UC: 89.6%; CD: 86.4%). 45.8% of patients not in remission at the time of conversion to VEDO sc were in remission at 6 months (UC: 50%; CD: 37.5%). Of the 74 patients with planned conversion to VEDO sc, 52 patients (70.3%) received VEDO sc as planned previously: 11.5% within the first 2 weeks, 42.3% after week 6, 19.2% after week 14, and 26.8% after six months or later. Conclusion IBD patients with a conversion from VEDO iv to VEDO sc show high effectiveness after 6 months; conversion usually was carried out between 6 and 14 weeks. Based on these data, VEDO sc is shown to be an effective alternative to VEDO iv in RWE and should therefore be considered an important option in treatment planning and discussion with patients.

Schlüsselwörter extraintestinale Manifestation - intraepitheliale Neoplasie - intestinale Komplikation - Immunsuppressiva - Primäre Sklerosierende Cholangitis

Abstract Background In this real-world-evidence (RWE) study we aimed to analyse the persistence of biologic therapy in biologic-naïve ulcerative colitis (UC) patients and to compare 1-year effectiveness of vedolizumab (VDZ) and anti-TNF. Methods Between 2017 and 2020, 1200 consecutively enrolled biologic-naïve and biologic- experienced patients with UC and Crohn′s disease (CD) were prospectively included in the VEDOIBD-Registry from 45 IBD-experienced centres across Germany. After exclusion of bio-experienced patients, CD and missing outcomes, the final sample consisted of 274 biologic-naïve UC-patients with 1-year follow-up data. Switchers of a drug were considered as treatment failure (modified intention-to-treat analysis; mITT) while switchers were excluded from per protocol analysis (PP). Clinical response modified (reduction of partial Mayo score (pMayo) from baseline to 1-year by >3 points or a reduction of at least 30% compared to baseline or reaching remission at 1-year) and (steroid-free) remission rates (pMayo ≤1 plus a bleeding subscore=0 (and no systemic use of steroids or budesonide at 1-year)) were predefined as outcomes. To reduce the effect of confounders, PS adjustment with inverse probability of treatment weighting (IPTW) was implemented. A weighted logistic regression was used, and the results were reported as odds ratio (OR) and 95% confidence interval (CI). Results 158 VDZ and 116 anti-TNF (ADA: 27.6%, IFX: 57.8%, GOL: 14.7%) biologic-naïve UC-patients were included in this prospective RWE comparing the effectiveness of VDZ vs anti-TNF. Until week 52 significantly more patients switched to another biologic-drug in the anti-TNF group than in the VDZ group (40.5% vs 16.5%; p<0.001) (Fig. 1). In mITT, clinical response at 1-year was significantly higher in VDZ than in anti-TNF treated patients (61.7% vs. 40.3%; OR 2.39 (95% CI 1.39–4.10)). VDZ also tended to be superior to anti-TNF for (steroid-free) remission (Tab. 1; p=0.058 (p=0.051)). In the PP-analysis, VDZ showed numerically higher 1-year effectiveness, but this did not reach statistical significance (Tab. 1). Analysing week-14 induction phase responders (Tab. 2), VDZ had numerically higher effectiveness rates compared to anti-TNF but without significant difference. Conclusion The 1-year maintenance findings suggested, in line with our previous induction phase data, only moderate long-term effectiveness in both groups. However, besides the significant response data, VDZ showed numerically higher remission rates compared to anti-TNF though only borderline significant. The higher treatment persistence of VDZ vs anti-TNF, along with the higher effectiveness, may suggest VDZ as a first-line biologic therapy option in UC patients.

Abstract Background Currently, faecal calprotectin (fCal) is considered the best available biomarker for both diagnosing and monitoring IBD. However, little is known about the stability of this protein in stool: The few studies available are contradictory. Our aim was to investigate the pre-analytical and biological variability of fCal in order to provide tools for its interpretation in the clinical setting. Methods Samples from 36 patients with IBD were collected to verify the preanalytical stability of fCal. Aliquots of homogenised stool were stored at room temperature and 37°C and fCal concentration measured for 7 consecutive days. In addition, fCal stability was assessed at each respective temperature in assay-specific extraction buffer. Results Baseline fCal concentration in stool samples varied from 14 to 2210µg/g. In aliquots or raw stool samples kept at room temperature, mean change from baseline on days 1, 4 and 7 was -30,95%, -43,66%, and -58,68%, respectively. This decline was irrespective of fCal concentration at baseline, but significantly reduced by using an assay-specific extraction buffer (Fig.1). Figure 1. Conclusion fCal is not stable at room temperature. Patients with IBD and their carers may be falsely reassured by low calprotectin values. Our results indicate that for preanalytical fCal handling, samples should only be stored at room temperature in the short term (up to 24 h). While refrigeration may be suitable for up to 48 h, the use of special extraction fluids improves fCal stability for a longer period. The sending of stool samples by post should therefore be avoided unless extraction buffer is used.