Diagnosing Congenital Sucrase-Isomaltase Deficiency in Children: An Algorithm Using Combined Breath Testing

Purpose: Disaccharidase deficiencies, including sucrase-isomaltase deficiency, can cause chronic gastrointestinal symptoms in children.While duodenal biopsies remain the diagnostic gold standard, results may be confounded by specimen handling variability or secondary mucosal injury.The noninvasive 13 C sucrose breath test ( 13 CSBT) accurately detects sucrase deficiency, including congenital sucrase-isomaltase deficiency (CSID), while the Trio-Smart breath test (BT) identifies small intestinal bacterial overgrowth (SIBO), a potential cause of secondary enzyme deficiency.Methods: We conducted a retrospective review of 25 pediatric patients with disaccharidase deficiencies on duodenal biopsy and normal villous architecture.Patients underwent 13 CSBT and/or Trio-Smart BT to evaluate for true CSID or SIBO.Clinical outcomes and treatment responses were assessed.Results: Of 21 patients with low sucrase activities who completed 13 CSBT, only 7 (33.3%)had abnormal results consistent with CSID.Six patients received sacrosidase, with three reporting symptom improvement.Of 15 patients who underwent Trio-Smart breath testing, 9 (60.0%) had abnormal results suggestive of SIBO and responded to antimicrobial treatment.Two patients had abnormal results on both tests.Interestingly, low palatinase levels were associated with abnormal 13 CSBT in some cases, though not consistently.Conclusion: Biopsy-based diagnosis may overestimate true CSID due to secondary causes or technical artifacts.Combined use of the 13 CSBT and Trio-Smart BT provides a noninvasive strategy to help distinguish primary or secondary sucrase deficiency, improving diagnostic accuracy and avoiding unnecessary lifelong enzyme therapy.We propose a diagnostic algorithm that integrates biopsy and BT results to guide evaluation and reduce misclassification of CSID.