Cystic fibrosis (CF) is a rare autosomal recessive disease whose etiology is due to mutations in the CFTR gene, leading to the transcription of a dysfunctional CFTR protein, which is the source of the clinical manifestations of the disease. The CFTR protein transports chloride and bicarbonate in secretory epithelia. It is most notably present in the airways, sweat glands, gastrointestinal tract (GI), pancreas, and vas deferens [1]. In the lungs, the production of abnormal secretions due to transporter dysfunction results in the formation of thick mucus, which reduces the effectiveness of clearance defense mechanisms and leads to progressive inflammatory and fibrotic damage [2]. In the pancreas, the thicker secretion causes successive obstructions in the pancreatic ducts, inflammation, and progressive tissue damage [1]. In the biliary tract, a similar process occurs, with thick bile secretion, cholestasis, and hepatic tissue damage [3].

There are also typical intestinal changes resulting from CF, associated with the involvement of its accessory organs. Evidence shows that various mechanisms triggered by CFTR mutation lead to alterations in the normal functioning of the GI tract, such as esophageal, gastric, and intestinal [4,5] dysmotility; increased proliferation of intestinal microorganisms associated with dysbiosis; and chemical modifications of the intestinal contents, such as lower pH, undigested nutrients, and metabolites produced by the gut microbiota [6].

All these manifestations clinically present as conditions typically associated with CF, including exocrine pancreatic insufficiency, CF-related liver disease, gastroesophageal reflux disease, distal intestinal obstruction syndrome, meconium ileus, cholelithiasis, and chronic constipation, among others [7].

Given this myriad of CF manifestations in the GI tract, abdominal symptoms such as abdominal pain, altered bowel habits, abdominal distension, and pain during defecation, among others, are quite common in people with CF [8]. Intestinal inflammation is a feature that can be associated both with the pathophysiological changes generated by the CFTR protein mutation and with the most common abdominal symptoms. Several studies have found endoscopic, histological, and biochemical evidence of inflammation in the intestines of people with CF and have proposed biological mechanisms to justify such inflammation [9].

Fecal calprotectin (FC) is a zinc- and calcium-binding protein found in the cytoplasm of macrophages and activated granulocytes and secreted by epithelial cells exposed to inflammatory cytokines or bacterial products, playing a significant role in the acute phase of inflammation [10]. It is found in the stool due to the migration of neutrophils to the intestines in response to the presence of pathogens and in other inflammatory conditions not mediated by microorganisms. As it is resistant to degradation by intestinal proteases, it remains stable in the intestinal lumen and in defecated feces. Although it is already established as a reliable method for assessing inflammation in inflammatory bowel disease, its role in CF is not yet fully elucidated. Lazarotto et al., in the most recent systematic review on the subject, highlight that research limitations such as small sample sizes or short follow-up periods, as well as the fact that CF is a multisystemic condition, make it more challenging to confirm that FC consistently and specifically reflects the level of intestinal inflammation in people with CF [11], reinforcing the importance of further studies on this marker in CF.

By systematically assessing abdominal complaints, biochemical analysis of the intestinal inflammation marker FC, and other common conditions in people with CF, this study aims to establish the prevalence of abdominal complaints in children with CF and investigate whether there is an association between abdominal symptoms, clinical conditions, and FC levels.

Twenty-two children participated in the study. Although many patients were eligible, few provided adequate stool samples. Furthermore, the study was funded to acquire the necessary supplies for analysis of stool samples from up to 22 participants, which was the main factor limiting the sample size. The most relevant characteristics of the sample are described in Table 1.

Only 4 participants (18.2%) had a BMI compatible with thinness (< 3rd percentile), one of whom also had short stature. Another 3 participants (13.6%) had a BMI compatible with overweight (> 85th percentile). All others (68.2%) had anthropometric measurements within the normal range for BMI and height (between 3rd and 85th percentiles for BMI and > 3rd percentile for height).

Regarding chronic antibiotic use, it is worth noting that the clinic follows Brazilian CF treatment guidelines, prescribing azithromycin three times a week to protect lung function and reduce pulmonary exacerbation risk, and recommends inhaled antibiotics (colistimethate sodium or tobramycin) for patients with airways colonized by P. aeruginosa [12]. The described antibiotic therapies were grouped under “chronic antibiotic use” in Table 1.

With respect to pancreatic enzyme replacement therapy (PERT), all participants diagnosed with exocrine pancreatic insufficiency reported consistent use of PERT, and none were taking proton pump inhibitors (PPI). In this clinic, PPI therapy is started to improve the effectiveness of PERT, mainly when the pancreatic enzyme dose is considered adequate, but the patient continues to show clinical or laboratory signs of poor digestion and nutrient absorption, which was not the case for any of the participants.

The two participants with CF-related liver disease had persistently elevated liver enzymes, mainly gamma-glutamyl transferase, and/or abnormalities on abdominal ultrasound following the Williams criteria. Possible etiologies such as drug toxicity, alpha-1 antitrypsin deficiency, Wilson’s disease, autoimmune hepatitis, viral hepatitis, and celiac disease were ruled out. Both study participants were asymptomatic regarding CF-related liver disease.

Although stool samples were collected from 22 participants, 3 brought samples at times when the team responsible for administering questionnaires was unavailable. In these cases, stools were collected, but questionnaires were not administered. Table 2 displays the participants’ questionnaire responses.

Among the participants who reported abdominal pain, the pain was most frequently located in the middle region of the abdomen, with most complaints centered in the mesogastrium (23%), followed by the right flank (18%), and both the left flank and right iliac fossa (14% each).

The distribution of the FC values found is described in Figure 1. The cut-off value suggested by the manufacturer, from which intestinal inflammation is considered present, is 50 mg/g. Only 3 participants (13.7%) showed normal levels of FC.

Fig. 1.

Distribution of CF measurements in the samplea.

a The cutoff value for intestinal inflammation is 50 mg/g. E: extreme values; Q3: third quartile; M2: mean; M1: median; Q1: first quartile.

To investigate whether there was an association between the level of intestinal inflammation and the presence of symptoms or other clinical characteristics, the Mann-Whitney test was applied. The results are shown in Table 3. There was no significant correlation between the continuous variables age (p = 0.73, Spearman rank correlation test), BMI percentile (p = 0.41, Spearman rank correlation test), height percentile (p = 0.057, Spearman rank correlation test), and pancreatic enzyme dose (p = 0.08, Spearman rank correlation test) and FC level. The median pancreatic enzyme dose used in the sample was 7126.24 (3860 – 11,905) IU/kg.

The measurement of fecal calprotectin in patients with CF indicated values related to intestinal inflammation in almost all cases. This was the most relevant finding of the present assessment. A total of 86.3% of patients showed FC levels above 50 mg/g, the cut-off value suggested by the manufacturer to increase sensitivity for intestinal inflammation, and the range most used in existing studies. Additionally, based on quantitative evaluation of FC in people with CF and controls, Jaudszus et al. [13] established a cut-off value of 44.1 mg/g to distinguish between the two groups, similar to the 50 mg/g used to indicate the presence of intestinal inflammation.

In healthy children, FC levels are higher in early months but decrease with age as intestinal immunity matures. Exposure to the intestinal microbiota, which begins to establish after leaving the uterus, and exposure to food antigens in a context where the intestinal mucosa functions as an immature barrier, promote the migration of granulocytes and macrophages rich in FC to the intestinal epithelium. From age 4 onwards, FC levels in healthy children begin to approach the adult normal range more rapidly, still maintaining the inverse correlation between age and FC level [14]. Even considering that the sample in the present study is pediatric, the increase in FC that can be attributed to immature immunity in children is quite discreet after age 4 and significantly lower than the results obtained, even among those without GI symptoms.

The finding of elevated FC levels in people with CF is consistent with related studies and with the theoretical framework proposed to explain intestinal inflammation caused by the disease.

Dysfunctional CFTR directly contributes to the genesis of intestinal inflammation by stimulating pro-inflammatory pathways in the intestinal inflammatory response [15,16]. and is associated with reduced efficacy of the innate immune response (low levels of beta-defensin 2, an antimicrobial protein), which can trigger a dysregulated immune response and a pro-inflammatory state [17]. Endoscopic evaluations have identified high concentrations of inflammatory interleukins and visualized mucosal changes throughout the GI tract, such as edema, enanthema, and ulcers [9]. Finally, the well-known intestinal dysbiosis in CF is characterized by a predominance of pro-inflammatory microorganisms, and the intestinal mucosa shows increased permeability due to changes in tight junctions, allowing the translocation of microorganisms and pro-inflammatory substances [16].

Several studies have sought associations between FC levels in people with CF and clinical manifestations. The evaluations show highly variable results. Rumman et al. [18]. found a reduction in fecal calprotectin levels associated with the use of inhaled antibiotics. Adriaanse et al. [19]. and Garg et al. [20] observed a negative correlation between age and calprotectin level. Parisi et al. [21] and Imanzadeh et al. [22] found a negative correlation between lung function and the presence of pulmonary exacerbation with FC levels. Schnapp et al. [23] and Imanzadeh et al. [22] found an association between systemic antibiotic therapy and reduced FC levels. Dhaliwal et al. [24] identified an inverse correlation between weight and height Z-scores and FC levels. Finally, Werlin et al. [25] identified a relationship between exocrine pancreatic insufficiency and higher FC levels.

The present research did not find an association or correlation between symptoms or clinical characteristics and FC levels. The analysis of the relationship between FC levels and the clinical features of flatulence, pulmonary exacerbation, colonization by P. aeruginosa, and pancreatic insufficiency nearly reached statistical significance, which would be biologically plausible and aligns with findings from other studies [11]. Frequent pulmonary exacerbations and colonization by P. aeruginosa are well-established associations in cystic fibrosis. The large amounts of airway secretions produced during these exacerbations, when swallowed, can raise fecal calprotectin levels simply because the calprotectin present in airway secretions reaches the colon [21]. The absence of associations or correlations may arise from a limitation of this study, namely, the reduced number of participants. Almost all the cited studies included more than 30 participants, which confers greater power in observing statistical significance and allows for more consistent conclusions.

It is important to highlight the reasons why the present sample size was so small. The main reason was funding for FC quantification tests, which are not part of the laboratory exams offered by the institution. The authors had to stop including participants in the study once they reached the number of tests available. Other, less significant factors included participants dropping out due to the inconvenience of collecting, storing, and transporting stool samples, improper home storage, or personal reasons. Such difficulties, especially in places with limited funding for science, reinforce the importance of seeking partnerships to organize multicenter studies and obtain more precise and conclusive results.

The most common abdominal symptoms were abdominal pain and flatulence, with each affecting about half of the participants. Pain is a recurrent symptom that became more noticeable after control of more severe morbidities in these patients. Studies indicate a high prevalence of this complaint in children with CF, with abdominal pain being the main manifestation in most cases, reported by up to 60% of patients [8]. In Brazil, there are no records of systematic studies on gastrointestinal symptoms in people with CF.

The evaluation and management of pain in children with CF are essential since painful symptoms may limit the patient’s participation in disease-related care and negatively impact their well-being and quality of life [26]. Additionally, abdominal symptoms in general are associated with mental health disorders in adolescents and adults with CF [27].

Besides the gastrointestinal comorbidities known to be associated with CF and intestinal inflammation—which did not show an association with symptoms in this study—other mechanisms may justify such manifestations in people with CF. Dysfunctional CFTR is expressed in neurons of the enteric nervous system, responsible for mediating vascularization, intestinal motility, secretion and absorption of substances, and intestinal inflammation, possibly contributing to the onset of gastrointestinal symptoms [28].

In adults with CF, functional GI disorders are more prevalent [29]. In the pediatric population, Smith et al. evaluated the prevalence of functional disorders described by ROME VI criteria in people aged 0 to 18 years, finding a statistically significant association between FC and a higher occurrence of functional abdominal pain diagnosis [30]. Disorders of the brain-gut axis are therefore also causes of abdominal symptoms in these individuals and may be associated with the abdominal pain reported by study participants.

This study demonstrates a high prevalence of intestinal inflammation measured by FC levels in children with CF at a Brazilian reference center for disease treatment. Despite the frequent occurrence of abdominal symptoms, it was not possible to establish a significant association between FC levels and clinical manifestations or gastrointestinal symptoms. The small sample size makes it hard to analyze a multifactorial outcome such as GI symptoms. These findings contribute to the understanding of gastrointestinal manifestations in CF patients. The authors highlight the importance of systematic investigation of these symptoms to better understand the impact of CF on pediatric patients. Therapeutic strategies that manage to mitigate such manifestations would have high potential to improve their quality of life.

This work was supported by the State University of Campinas Teaching Research and Extension Support Fund (FAEPEX), and JDR receives CNPq Research Productivity Grant (#300024/2025-8) - CNPq: Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazilian National Council for Scientific and Technological Development).

The data that support the findings of this study are available from the corresponding author.