Highlights
- Fecal calprotectin (FC) is a promising non-invasive biomarker for gastrointestinal graft-versus-host disease (GI-GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT).
- FC shows moderate to high predictive accuracy for GI-GVHD around day +21 post-transplant and correlates with endoscopic severity at diagnosis.
- FC levels significantly decrease after effective treatment, making it a useful tool for disease monitoring, including identifying treatment response.
- Concurrent infections can elevate FC levels but do not significantly diminish its discriminative ability, underscoring the need for clinical context in interpretation.
Background
Gastrointestinal graft-versus-host disease (GI-GVHD) remains a major complication following allogeneic hematopoietic stem cell transplantation (allo-HSCT), affecting over half of recipients and substantially contributing to morbidity and mortality. Clinical symptoms such as diarrhea, abdominal pain, and bleeding are nonspecific and overlap with infectious or drug-related etiologies. Endoscopic evaluation with histological confirmation is the gold standard for diagnosis but is invasive, resource-intensive, and may not be feasible in all patients due to clinical instability.
Calprotectin, a neutrophil-derived calcium-binding protein abundant in feces during intestinal inflammation, has emerged as a validated biomarker in inflammatory bowel diseases. Its utility in the allo-HSCT setting, particularly for GI-GVHD, attracted research interest as a non-invasive, readily measurable marker to aid early diagnosis, disease severity assessment, and therapeutic monitoring, potentially mitigating reliance on invasive procedures.
Key Content
Chronological Development of Evidence
The earliest prospective investigations, such as the study by Kovacs et al. (2015), assessed fecal calprotectin in 51 allo-HSCT patients, observing significantly elevated FC levels in those developing GI-GVHD. Particularly, higher FC concentrations correlated with more severe GI-GVHD grades, offering preliminary evidence that fecal calprotectin might serve as a non-invasive screening tool to distinguish GVHD from other causes of intestinal symptoms. Alpha-1 antitrypsin was also assessed but did not independently associate with GI-GVHD.
Building on this foundation, Piñero-Pérez and colleagues (2026) performed a larger prospective observational study involving 165 adult allo-HSCT recipients, systematically measuring FC on days +7, +14, +21 post-transplant, at GI-GVHD onset, and seven days after treatment initiation. This design allowed evaluation of FC as a predictive biomarker, a diagnostic adjunct, and a monitoring tool.
Predictive Value of Early FC Measurements
The Piñero-Pérez study demonstrated that FC measured as early as day +7 post-transplant had no predictive value for GI-GVHD, with area under the curve (AUC) = 0.50, indicating no discrimination beyond chance. At days +14 and +21, predictive accuracy improved, with AUCs of 0.69 and 0.77, respectively. The optimal cutoff at day +21 was 52.5 µg/g, yielding 75% sensitivity and 87% specificity for later development of biopsy-confirmed GI-GVHD. These findings suggest that serial FC measurements, especially beyond the second week, can aid risk stratification and early intervention decisions.
Diagnostic Correlations at Onset
At GI-GVHD diagnosis, median FC levels were markedly elevated (median 120 µg/g), significantly correlating with the endoscopic grading of lesion severity (Spearman r = 0.31, p = 0.02) but not with clinical or histological grades. This indicates fecal calprotectin reflects mucosal inflammation extent observed endoscopically more reliably than symptom severity or histologic staging, potentially due to sampling variability or disease patchiness.
Monitoring and Treatment Response
FC levels showed a significant decline after seven days of treatment (from median 120 to 51.5 µg/g, p = 0.04), consistent with response to immunosuppressive therapy. Importantly, the presence of concurrent gastrointestinal infections elevated FC values, yet these elevations did not impair FC’s ability to discriminate GI-GVHD, provided clinical and microbiological data were integrated.
Biological Mechanisms and Translational Implications
Calprotectin is a heterodimer of S100A8/S100A9 proteins predominantly released by activated neutrophils and monocytes. It binds divalent metal ions, contributing to antimicrobial defense and modulating inflammatory cascades. In GI-GVHD, donor-derived immune cell attack induces epithelial and endothelial injury, stimulating innate immune cell infiltration and calprotectin release. The fecal concentration reflects neutrophil-mediated mucosal inflammation, providing a biological rationale for its elevation and utility as a biomarker.
Expert Commentary
The accumulating evidence supports fecal calprotectin as a dynamic and non-invasive biomarker complementing clinical and endoscopic assessment in GI-GVHD. Its strengths include easy sampling, reproducibility, and correlation with mucosal inflammation severity. However, several challenges temper widespread clinical adoption.
Firstly, FC’s limited specificity remains a concern; elevations occur in various inflammatory and infectious conditions common in immunocompromised hosts, including cytomegalovirus colitis, bacterial enterocolitis, and neutropenic enteropathy. Thus, FC must be interpreted within the full clinical context, supplemented by microbial investigations and, when feasible, histology.
Secondly, inter-study heterogeneity in FC cutoff values and timing underlines the need for standardized protocols and multicenter validation. Although day +21 measurement showed superior predictive accuracy, earlier detection remains elusive, warranting further exploration of combined biomarker panels or serial trend analyses.
Thirdly, the moderate correlation with endoscopic but not histologic or clinical grading reflects the complex pathophysiology of GI-GVHD, with mucosal damage not always mirrored by clinical symptoms or patchy histology. Indeed, calprotectin might preferentially reflect neutrophil-driven inflammation over lymphocytic infiltration captured histologically.
Overall, FC should be embedded into a multimodal diagnostic algorithm rather than viewed as a standalone test. Future research might investigate integration with other fecal biomarkers (e.g., alpha-1 antitrypsin, lactoferrin), serum cytokines, or advanced imaging for composite risk assessment.
Conclusion
Fecal calprotectin is a promising non-invasive biomarker for predicting, diagnosing, and monitoring gastrointestinal graft-versus-host disease following allo-HSCT. It correlates with endoscopic severity and responds to treatment, providing real-time insights into mucosal inflammation dynamics. While concurrent infections and other inflammatory conditions can elevate FC, careful clinical integration preserves its discriminative utility. Incorporation of fecal calprotectin measurement into clinical workflows could reduce reliance on invasive endoscopy, enable earlier intervention, and improve patient management.
Nevertheless, limitations in specificity and variability across studies highlight the necessity for further prospective multicenter validation and standardization of assay timing and cutoff thresholds. Combining FC with other emerging biomarkers and clinical data promises to enhance the accuracy and applicability of GVHD diagnostics in the evolving transplant landscape.
References
- Piñero-Pérez C, Velasco-Guardado A, Pérez-López E, Cortés-Rodríguez M, Cabrero-Calvo M, Martín-López AA, Sánchez-Guijo F, López-Corral L. Fecal calprotectin as a biomarker for the diagnosis of gastrointestinal graft-versus-host disease following allogeneic hematopoietic stem cell transplantation. Bone Marrow Transplant. 2026 Jun 23. PMID: 42332220.
- Kovacs J, et al. Fecal calprotectin as a biomarker of intestinal graft versus host disease after allogeneic hematopoietic stem cell transplantation. Sci Rep. 2015 Jan 21;5:7920. PMID: 25605402.
- De Filippo MR, et al. Biomarkers for diagnosis and management of graft-versus-host disease: A comprehensive review. Am J Hematol. 2022;97(7):920-939. PMID: 35121236.
- Zeiser R, Blazar BR. Gastrointestinal graft-versus-host disease: pathogenesis, diagnosis, and treatment. Hematology Am Soc Hematol Educ Program. 2013;2013:398-403. PMID: 24319245.
