Table 1. Application of pathophysiology-actionable biomarker approach to managing patients with IBS.

(derived from ref. 65, Gut 2020;69:1730-1737)

Pathophysiology	Diagnostic test	Actionable biomarker
Evacuation disorders	Anorectal manometry, balloon expulsion, ? defecography	Spastic pelvic floor or descending perineum
Transit	Radiopaque markers, scintigraphy, wireless motility capsule	Accelerated transit at 24h or delayed transit at 48h on scintigraphy
Sensation and central nervous system hypervigilance	Rectal sensation to balloon distension, e.g., during anorectal manometry (ARM)	Rectal sensation recorded during ARM as symptoms: first sensation, gas, urge, pain
Psychosocial factors	HAD, IBS-QOL, PAC-SYM, PAC-QOL	Anxiety, depression, general pain conditions
Bile acid diarrhea	Serum 7αC4, primary or total bile acids (single or 48h stool), 75-SeHCAT retention	Increased bile acid synthesis or excretion
Disaccharidase deficiency	Lactose-hydrogen breath test, duodenal biopsy measurements of disaccharidases	Lactose and sucrose intolerance with objective test results
Celiac disease	TTG-IgA, anti-gliadin IgA	Diagnostic tests for coeliac disease
Local immune reactions to foods or mucosal inflammation	Fecal calprotectin, careful dietary history, specific inquiry on fructans and galactans, consider gluten intolerance	Colonoscopy for microscopic colitis, experimental studies, screen for HLA DQ2/8 with gluten intolerance in absence of proven celiac disease
Microbiome	N/A	N/A

HAD=Hospital Anxiety and Depression scale; IBS-QOL=Irritable Bowel Syndrome-Quality of Life questionnaire; PAC-SYM= Patient Assessment of Constipation-Symptoms questionnaire; PAC-QOL= Patient Assessment of Constipation-Quality of Life questionnaire; N/A=not applicable; 7αC4=7α-hydroxy-4-cholesten-3-one; 75-SeHCAT=75-selenium homocholic acid taurine; TTG = tissue transglutaminase; HLA DQ2/8= human leukocyte antigen DQ2/8