Table 3 Assessment of normal gut function^a

Subjective assessments of well-being

Validated questionnaires useful to assess quality of life and gut health

IBS-Quality of Life (IBS-QOL)

Validated for assessment of quality of life specific to IBS: 34 questions

Inflammatory Bowel Disease Questionnaire (IBDQ)

Validated for assessment of health-related quality of life (HRQoL) in adult patients with IBD

Bowel Disease Questionnaire (BDQ)

Validated to distinguish patients with functional and organic GI disease

Health Status Questionnaire (HSQ-12)

Validated for assessment of HRQoL in the general population

Short Form Health Survey SF-12 (SF-12)

Validated for assessment of HRQoL in the general population

GI symptom scores

IBS Severity Scoring System (IBS-SSS)

Validated for scoring lower GI symptoms on the basis of nine questions; range of 0 to 500 points

Short Form Leeds Dyspepsia Questionnaire (SF-LDQ)

Validated instrument for measuring the presence and severity of dyspepsia

Gastrointestinal Symptom (GIS) profile

Validated for assessment of symptoms of functional dyspepsia; 10 questions

Subject's Global Assessment of Relief (SGA)

Validated assessment of the impact of treatment on IBS-related symptoms; 1 question

IBS Global Assessment of Improvement (IBS-GAI) ("adequate relief")

Asks participants if, compared to the way they felt before entering the study, their IBS symptoms have changed over the past 7 days; 1 question

Functional Bowel Disorder Severity Index (FBDSI)

Validated score for assessment of patient perception of abdominal pain in IBS

Numeric Rating Scale (NRS) for assessment of pain

Validated in IBS patients

Visceral Sensitivity Index (VSI)

Validated psychometric instrument that measures GI symptom-specific anxiety

Bristol Stool Scale/Bristol Stool Chart

A medical aid designed to classify the form of human faeces into seven categories

Gastrointestinal Symptom Rating Scale

Eating habits

Food frequency questionnaire

7-day diet history assessed using computer software

Objective parameters

Markers of functionality

Gastric function

pH metry in the esophagus [6, 7] and stomach [1–3], gastroesophageal reflux episodes (< 50/day, <60 minutes total), viscosity of the luminal content using a viscometer, stool weight (> 100 g/d, <500 g/d) and stool consistency (water content)

Permeability measurements

Tracer molecules (lactulose/mannitol, ⁵¹Cr-EDTA, PEG);

Motility tests

Barostat, gastric scintigraphy, ¹³C urea breath test (gastric emptying) and lactulose hydrogen breath test (normal range: 40 to 240 hours)

Transit time

Radiopaque pellets (Hinton test) and isotope-labelled test meal (normal range: 24 to 168 hours)

Digestion parameters

Stool elastase (> 200/g) and stool fat (< 7 g/d), carbohydrate breath tests, anthropometry and micronutrient analysis

Markers of intestinal integrity

Epithelial integrity

Histology (villus height/crypt depth ratio, mitosis and apoptosis), mucus secretion (mucins and trefoil peptides) and Ussing chamber (ion fluxes and electric potentials)

Specific molecules

E-cadherin, growth factors, tight junction molecules, α₁-antitrypsin in faeces and LPS in blood

Antimicrobial peptides

α- and β-defensins, calprotectin, lysozyme or neutrophil-derived elastase in faeces

Marker of intact immunity

Cell counts and phenotyping

Differential blood count and FACS analysis, histopathology of intestinal biopsies and immunohistochemistry of intestinal biopsies

Cell mediators and cytokines

Inflammatory cytokines (IL-1, IL-6 and TNFα), anti-inflammatory cytokines (IL-10 and TGFβ), regulatory cytokines (IL-2, sIL-2R, IL-4, IL-5 and so on), proteases (tryptase, chymases, chymotrypsin and so on), immunoglobulins (IgA, sIgA and IgE) and others (retinoic acid, neuropeptides and so on)

Functional assays

Cell cultures and cocultures, DTH response, phagocytosis, chemotaxis, oxidative burst (superoxide anion generation) and NK cell activity

Analysis of the intestinal microbiome

Classical approaches

Bacterial culture and toxin measurements

New approaches

Metagenomics (PCR and full bacterial sequencing), metabonomics (metabolic capacity of the microbiome)