Chronic rhinosinusitis with nasal polyps (CRSwNP) is a persistent inflammatory disorder of the nasal and paranasal sinus mucosa characterized by polyp formation, nasal obstruction, rhinorrhea, facial pressure and loss of smell, with a substantial impact on quality of life and healthcare utilization [1]. In Europe, CRSwNP is estimated to affect around 1-2% of the population and many patients experience a relapsing course requiring long-term intranasal corticosteroids, intermittent systemic corticosteroids, and, in severe cases, repeated endoscopic sinus surgery [2]. Contemporary guidelines emphasize that CRSwNP is heterogeneous and frequently driven by type-2 (T2) inflammation, a pathway commonly associated with eosinophilic infiltration and elevated T-helper-2 cytokines such as interleukin (IL)-4, IL-5 and IL-13 [1,3]. Within this framework, IL-5 has a central role in eosinophil differentiation, survival and tissue recruitment, making it a key mediator of polyp inflammation and persistence [4]. A major clinical challenge is the objective assessment of “disease control” and treatment response over time. EPOS and EUFOREA have proposed harmonized concepts and definitions (including control, remission, recurrence/exacerbation, and disease modification) to support treat-to-target strategies and standardized monitoring [3]. Despite these efforts, routine practice still relies heavily on symptom scores, endoscopic polyp grading, imaging when needed and history of systemic corticosteroid use or surgery, measures that may not fully capture underlying inflammatory activity or predict relapse [1,3]. Therefore, there is increasing interest in blood-based biomarkers that are minimally invasive, reproducible and reflective of endotype activity, enabling improved stratification of patients and earlier identification of uncontrolled disease. IL-5 is particularly relevant because clinical benefit from targeting the IL-5 axis supports its pathogenic importance in CRSwNP. Early proof-of-concept work showed that anti-IL-5 therapy could reduce polyp burden in selected patients and that local IL-5 levels were associated with treatment response [5]. More recently, randomized phase 3 trials demonstrated that mepolizumab (anti-IL-5) improved outcomes such as nasal polyp size and nasal obstruction in patients with severe, recurrent, refractory CRSwNP [6]. Likewise, benralizumab (anti-IL-5 receptor α) improved nasal polyp score and nasal blockage compared with placebo, reinforcing the clinical value of the IL-5 pathway as a therapeutic and biologic target [7]. In parallel, other type-2 biologics (e.g., dupilumab targeting IL-4/IL-13 signaling) also produce substantial improvements in polyp size and symptoms, highlighting the importance of type-2 inflammation in many patients [8]. Calprotectin, a heterodimer of S100A8/S100A9, is an innate immune protein abundant in neutrophils and monocytes and is widely used as a marker of inflammatory activity in several diseases [9]. In CRSwNP, emerging evidence suggests that calprotectin-related pathways may reflect aspects of non-type-2 inflammation, epithelial-innate immune dysregulation and tissue remodeling, complementing classic type-2 biomarkers [10-12]. Clinical studies have reported elevated circulating calprotectin in chronic rhinosinusitis and correlations with symptom burden, supporting its candidacy as a systemic inflammatory biomarker [9]. Together, circulating IL-5 (as a type-2 activity marker) and calprotectin (as an innate inflammatory marker) may provide a more complete biologic picture of disease activity and help link immunologic endotypes to real-world disease control in CRSwNP.

This study was conducted as a hospital-based case-control study in Baghdad, Iraq (Imam Ali Hospital, Al-Kindy Teaching Hospital), over a period extending from 1 February 2024 to 31 March 2025 in otorhinolaryngology (ENT) patient managing patients with chronic rhinosinusitis. The primary objective was to evaluate circulating calprotectin and interleukin-5 (IL-5) as biomarkers of type-2 inflammation and to assess their association with disease control in chronic rhinosinusitis with nasal polyps (CRSwNP).

Study Population

A total of 60 participants were enrolled and allocated into two groups:

• Case group (n = 30): Patients with a confirmed diagnosis of chronic rhinosinusitis with nasal polyps

• Control group (n = 30): Apparently healthy individuals without clinical or endoscopic evidence of chronic rhinosinusitis or nasal polyps

Cases and controls were frequency-matched for age and sex to reduce potential confounding.

Diagnostic Criteria

The diagnosis of CRSwNP was established in accordance with internationally accepted criteria. Patients had sinonasal symptoms lasting ≥12 weeks, including nasal obstruction, nasal discharge, facial pressure, and/or reduction or loss of smell, together with bilateral nasal polyps confirmed by nasal endoscopy performed by an experienced ENT specialist.

Assessment of Disease Control

Disease control in CRSwNP patients was evaluated based on clinical assessment and endoscopic findings, in line with contemporary guideline concepts of controlled and uncontrolled disease. Parameters included symptom severity, need for systemic corticosteroids and endoscopic polyp appearance.

Inclusion Criteria

• Age ≥18 years

• Confirmed diagnosis of CRSwNP (cases)

• Absence of sinonasal inflammatory disease (controls)

• Ability and willingness to provide written informed consent

Exclusion Criteria

• History of sinus surgery within the preceding 6 months

• Acute upper respiratory tract infection within 4 weeks prior to enrollment

• Use of systemic corticosteroids, biologic agents or immunosuppressive therapy within 4 weeks before blood sampling

• Presence of bronchial asthma, autoimmune disease, malignancy or other chronic inflammatory or infectious conditions

• Pregnancy or lactation

Data Collection

All participants underwent standardized evaluation, including demographic data (age and sex) and relevant medical history. Patients in the case group received a detailed ENT examination, including nasal endoscopy.

Blood Sampling and Laboratory Analysis

Venous blood samples (5 mL) were collected from all participants under aseptic conditions. Samples were centrifuged and serum was separated and stored according to standard laboratory protocols until analysis.

• Serum calprotectin levels were measured using a commercially available enzyme-linked immunosorbent assay (ELISA) kit following the manufacturer’s instructions

• Serum IL-5 concentrations were determined using a validated ELISA method with established analytical sensitivity

All assays were performed in duplicate and internal quality control measures were applied.

Statistical Analysis

Statistical analysis was conducted using SPSS software. Continuous variables were presented as mean±standard deviation (SD) or median (interquartile range) based on data distribution, while categorical variables were expressed as number (percentage). Comparisons between cases and controls were performed using the independent samples t-test or Mann-Whitney U test, as appropriate. Associations between biomarker levels and disease control parameters were evaluated using correlation analysis. A p-value <0.05 was considered statistically significant.

Table 1 shows that the demographic characteristics of the study population were comparable between patients with chronic rhinosinusitis with nasal polyps (CRSwNP) and the control group. The mean age did not differ significantly between cases (42.6±9.3 years) and controls (41.1±8.7 years) (p = 0.523). Similarly, the sex distribution was well balanced, with males constituting 60.00% of the CRSwNP group and 56.67% of the control group (p = 0.795). Smoking status also showed no statistically significant difference between the two groups, as 30.00% of CRSwNP patients and 20.00% of controls were current smokers (p = 0.371).

Table 1: Demographic characteristics of the study population

Table 2 summarizes the clinical presentation, disease control status and endoscopic severity among patients with chronic rhinosinusitis with nasal polyps (CRSwNP). The majority of patients presented with prominent sinonasal symptoms, most notably nasal obstruction (86.67%) and hyposmia or anosmia (80.00%), reflecting the significant impact of polyp disease on nasal airflow and olfactory function. Rhinorrhea was reported in nearly three-quarters of patients (73.33%), while facial pressure was present in 60.00%, indicating substantial sinonasal inflammatory burden. Assessment of disease control revealed that fewer than one-third of patients (30.00%) were classified as controlled, whereas 26.67% were partially controlled and a considerable proportion (43.33%) had uncontrolled disease. This distribution highlights the chronic and often refractory nature of CRSwNP, with a large subset of patients experiencing persistent symptoms despite standard management. Endoscopic evaluation demonstrated moderate to severe disease in most cases, as 36.67% of patients had grade 2 polyps and 40.00% had grade 3 polyps, while only 23.33% exhibited mild (grade 1) disease. Collectively, these findings indicate that the study population predominantly consisted of patients with clinically significant, poorly controlled CRSwNP and substantial endoscopic disease severity, providing an appropriate context for evaluating the relationship between inflammatory biomarkers and disease control.

Table 2: Clinical characteristics, disease control status and endoscopic 

Table 3 demonstrates a clear and statistically significant elevation of both serum calprotectin and IL-5 levels in patients with chronic rhinosinusitis with nasal polyps (CRSwNP) compared with healthy controls. Mean serum calprotectin levels were markedly higher in CRSwNP cases than in controls (412.6±118.4 vs. 186.3±72.9 ng/mL; p <0.001), indicating a pronounced inflammatory burden in affected patients. Similarly, serum IL-5 levels were significantly increased in CRSwNP patients compared with controls (9.84±3.12 vs. 3.96±1.85 pg/mL; p <0.001), reflecting enhanced type-2 inflammatory activity. Furthermore, within the CRSwNP group, uncontrolled disease was associated with substantially higher concentrations of both biomarkers compared with controlled disease. Uncontrolled CRSwNP patients exhibited significantly elevated serum calprotectin (462.9±104.7 vs. 268.7±86.5 ng/mL; p = 0.003) and IL-5 levels (10.96±2.87 vs. 5.21±1.94 pg/mL; p = 0.001).

Table 3: Comparison of serum calprotectin and IL-5 levels between study groups 

Table 4 illustrates a significant association between endoscopic nasal findings and serum levels of both calprotectin and IL-5. Patients with active inflammatory endoscopic features, particularly nasal polyps, demonstrated the highest biomarker levels, with mean serum calprotectin and IL-5 concentrations reaching 286.4±58.2 ng/mL and 24.6±6.1 pg/mL, respectively (both p <0.001). Similarly, the presence of mucosal edema and purulent discharge was associated with significantly elevated serum calprotectin and IL-5 levels compared with near-normal mucosa, reflecting ongoing mucosal inflammation and immune activation. In contrast, patients with near-normal mucosal appearance exhibited the lowest mean levels of both biomarkers (calprotectin: 148.3±32.6 ng/mL; IL-5: 11.2±3.1 pg/mL), indicating reduced inflammatory activity.

Table 4: Serum calprotectin and IL-5 levels according to endoscopic nasal findings

Table 5 shows a clear and statistically significant stepwise increase in serum calprotectin and IL-5 levels with worsening sinonasal symptom severity. Patients with mild symptoms exhibited the lowest mean concentrations of calprotectin (171.6±33.8 ng/mL) and IL-5 (13.4±3.0 pg/mL), whereas those with severe symptoms demonstrated markedly elevated levels (305.2±57.1 ng/mL and 26.5±6.2 pg/mL, respectively; p <0.001). This progressive rise across mild, moderate and severe categories indicates a strong correlation between symptom burden and systemic inflammatory activity, highlighting the role of these biomarkers in reflecting clinical disease severity.

Table 5: Serum calprotectin and IL-5 levels according to sinonasal symptom severity

Table 6 further supports this relationship by demonstrating a significant association between biomarker levels and olfactory function status. Patients with normal smell had the lowest serum calprotectin and IL-5 levels (168.9±31.5 ng/mL and 12.9±2.7 pg/mL, respectively), while those with hyposmia showed intermediate values. The highest levels were observed in patients with anosmia (308.7±55.4 ng/mL for calprotectin and 26.9±6.0 pg/mL for IL-5; p <0.001), suggesting that worsening olfactory dysfunction parallels increased inflammatory and type-2 immune activity. These findings emphasize the close link between loss of smell and underlying disease severity in CRSwNP.

Table 6: Serum biomarker levels according to olfactory function status

Table 7 demonstrates that serum calprotectin and IL-5 levels are significantly influenced by the history of systemic corticosteroid use. Patients with no prior steroid use had the lowest biomarker levels, whereas those with intermittent and frequent corticosteroid use exhibited progressively higher concentrations, with the highest levels seen in the frequent-use group (calprotectin: 311.8±57.3 ng/mL; IL-5: 27.6±6.1 pg/mL; p = 0.004 and p = 0.002, respectively). This pattern likely reflects greater baseline disease severity and recurrent inflammatory activity in patients requiring repeated systemic therapy. Collectively, Tables 5-7 reinforce the utility of serum calprotectin and IL-5 as objective biomarkers that correlate closely with symptom severity, functional impairment and treatment burden in CRSwNP.

Table 7: Serum biomarker levels according to history of systemic corticosteroid use

In the present study, patients with chronic rhinosinusitis with nasal polyps (CRSwNP) and healthy controls were comparable regarding age, sex distribution and smoking status (Table 1), minimizing the potential influence of demographic confounders on biomarker interpretation. Similar demographic homogeneity has been reported in several CRSwNP cohorts, supporting the concept that disease severity and activity are primarily driven by inflammatory endotypes rather than baseline characteristics [1,2]. CRSwNP is now recognized as a heterogeneous inflammatory disorder in which clinical presentation, severity and treatment response reflect distinct immunopathological mechanisms [3]. Clinically, the majority of CRSwNP patients in this study exhibited prominent nasal obstruction and olfactory dysfunction (Table 2), which are hallmark symptoms of polypoid disease and major determinants of impaired quality of life [4,5]. The high proportion of partially controlled and uncontrolled cases, together with moderate-to-severe endoscopic polyp grades, underscores the refractory nature of CRSwNP in a substantial subset of patients. This observation is consistent with previous studies indicating that despite intranasal corticosteroids, intermittent systemic therapy and surgery, many patients continue to experience persistent symptoms and recurrent inflammation [6-8]. A key finding of this study is the significant elevation of serum calprotectin and IL-5 levels in CRSwNP patients compared with controls (Table 3). IL-5 is a pivotal type-2 cytokine responsible for eosinophil differentiation, activation and survival and its role in CRSwNP pathogenesis has been well established [9-11]. Elevated IL-5 levels have been associated with tissue eosinophilia, polyp recurrence, disease severity and poor response to conventional therapies [12]. In contrast, calprotectin (S100A8/A9), a marker of neutrophil activation and innate immune response, reflects a non-type-2 or mixed inflammatory pattern and has been increasingly recognized in refractory CRSwNP [13,14]. The simultaneous elevation of both biomarkers in our cohort supports the concept that severe CRSwNP often represents a mixed eosinophilic-neutrophilic inflammatory phenotype rather than a purely type-2 process [3,15]. Importantly, within the CRSwNP group, uncontrolled disease was associated with significantly higher serum IL-5 and calprotectin levels compared with controlled disease (Table 3). This finding is in strong agreement with recent evidence demonstrating that elevated inflammatory biomarkers correlate with disease non-control and higher symptom burden [16]. De Corso et al. showed that increased IL-5 and calprotectin levels were strongly associated with uncontrolled CRSwNP, emphasizing IL-5 as a particularly robust marker of severe, difficult-to-treat disease [16]. These data collectively support the potential clinical utility of inflammatory biomarkers for identifying patients at risk of poor disease control. The relationship between biomarker levels and endoscopic findings observed in this study (Table 4) further reinforces their pathophysiological relevance. Higher serum IL-5 and calprotectin levels were observed in patients with nasal polyps, mucosal edema and purulent discharge compared with those with near-normal mucosa. Similar associations between inflammatory mediator levels and endoscopic severity have been reported previously, indicating that biomarker elevation parallels the extent of local mucosal inflammation [17-19]. Purulent discharge and edema may also reflect microbial dysbiosis and secondary bacterial colonization, which can amplify innate immune activation and neutrophilic inflammation, thereby increasing calprotectin levels [20,21]. The stepwise increase in serum calprotectin and IL-5 with worsening sinonasal symptom severity (Table 5) and olfactory dysfunction (Table 6) highlights the close link between systemic inflammatory activity and clinical expression of CRSwNP. Smell loss is a key marker of severe disease and has been emphasized in current severity classifications and treatment algorithms [22,23]. Previous studies have shown that olfactory impairment correlates with higher eosinophilic inflammation and increased expression of type-2 cytokines, particularly IL-5 [24,25]. Our findings extend these observations by demonstrating that systemic biomarker levels reflect functional impairment, suggesting a potential role for serum biomarkers in monitoring disease impact. Furthermore, patients with a history of frequent systemic corticosteroid use exhibited the highest serum IL-5 and calprotectin levels (Table 7). This association likely reflects greater baseline disease severity rather than a direct effect of corticosteroids on biomarker production. Frequent systemic steroid use is widely recognized as a surrogate marker of uncontrolled or severe CRSwNP and is a key criterion for considering advanced therapies, including biologics [22,26]. Persistent elevation of IL-5 despite repeated systemic therapy supports the rationale for targeting IL-5 or upstream type-2 pathways in selected patients [27-29]. From a clinical perspective, these findings suggest that serum IL-5 and calprotectin may serve as accessible biomarkers reflecting disease activity, severity and treatment burden. While tissue and nasal secretion biomarkers more directly represent local inflammation, serum markers may offer a practical alternative for routine assessment, especially when integrated with clinical and endoscopic evaluation [30,31]. Nevertheless, biomarker interpretation should be cautious, as discordance between systemic and local inflammatory markers has been reported, emphasizing the need for multimodal assessment [32]. This study has some limitations, including the relatively small sample size and the absence of additional type-2 biomarkers such as IL-4, IL-13, periostin or tissue eosinophil counts. Moreover, serum-based measurements may not fully capture localized sinonasal immune responses. Future studies should incorporate combined serum, nasal secretion and tissue analyses, evaluate biomarker cut-off values and explore their predictive value for recurrence and response to biologic therapy in larger prospective cohorts [11,16,33]. 

In conclusion, the present study demonstrates that elevated serum IL-5 and calprotectin levels are closely associated with disease presence, severity, poor control, endoscopic inflammation, symptom burden, olfactory dysfunction and systemic corticosteroid requirement in CRSwNP. These findings are consistent with current literature supporting the role of inflammatory biomarkers in characterizing disease endotypes and identifying patients with severe, difficult-to-treat CRSwNP. Integration of serum biomarkers into clinical assessment may contribute to more individualized disease stratification and optimized therapeutic decision-making.

Ethical Approval

Ethical approval was obtained from the relevant institutional review board in Baghdad. The study was conducted in accordance with the Declaration of Helsinki and written informed consent was obtained from all participants prior to inclusion. Participant confidentiality and data protection were strictly maintained.

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