Conceptual and operational consistency in defining intestinal failure across randomized controlled trials: a systematic review and meta-research analysis

Intestinal failure (IF) is a rare but serious condition associated with high morbidity, mortality, and healthcare resource use. Although consensus-based definitions for IF exist, their adoption in randomized controlled trials (RCTs) remains uncertain. This variability compromises the comparability of evidence and hinders the development of robust clinical guidelines. The aim of this study was to examine the conceptual and operational consistency of IF definitions in RCTs, assess methodological and reporting quality, and explore implications for research synthesis and clinical decision-making. Systematic review of RCTs. We searched PubMed/MEDLINE, Embase, Web of Science, and Scopus up to May 2025 for RCTs involving participants with IF. Two reviewers independently extracted data, focusing on the presence and nature of IF conceptual and operational definitions, and assessed methodological and reporting quality. Studies were categorized by quality thresholds defined a priori. From 9354 records screened, 12 RCTs (2011–2025) involving 617 participants with IF were included. Most were conducted in high-income countries and focused on adults, although some involved pediatric short bowel syndrome (SBS) and intestinal failure-associated liver disease populations. Only 3 trials (25%) provided an explicit, ESPEN-aligned conceptual definition of IF, integrating both functional classification and parenteral support (PS) dependency. The majority (66.7%) relied solely on operational thresholds, most often PS frequency (≥ 3 days/week) and duration (≥ 12 months), without conceptual framing, while 4 trials (33.3%) incorporated surrogate markers such as fecal output ≥ 1500 g/day or bowel length without confirming PS dependence. Two trials (16.7%) lacked any explicit definition. Variability extended to terminology, inclusion thresholds, and conflation of SBS with IF. Definitions of IF in RCTs remain heterogeneous, with frequent divergence from consensus standards and variable study quality. This heterogeneity in IF definitions fundamentally limits evidence synthesis and reduces the clinical applicability of trial findings. Establishing and enforcing harmonized, consensus-driven definitions is not merely a methodological refinement but an urgent necessity to build a reliable evidence base for this high-impact condition.