GI Effects Comprehensive Profile – 1 Day (Stool)

Calprotectin is a calcium- and zinc-binding protein released by neutrophils that infiltrate the intestinal mucosa during inflammation. Its concentration in stool correlates with the degree of mucosal leucocyte activity, making it a sensitive marker of intestinal inflammation. The protein is stable in stool at room temperature for several days, which facilitates home collection.

Elevated faecal calprotectin distinguishes organic inflammatory bowel disease from functional disorders and is used to monitor disease activity in Crohn disease and ulcerative colitis. Modest elevations can also accompany non-steroidal anti-inflammatory drug enteropathy, intestinal infection, and coeliac disease.

Secretory IgA is the predominant immunoglobulin in mucosal secretions, formed when dimeric IgA produced by plasma cells in the lamina propria binds to the polymeric immunoglobulin receptor on epithelial cells and is transported across the epithelium. It plays a key role in pathogen neutralisation and regulation of commensal microbiota without activating pro-inflammatory cascades.

Low faecal sIgA may reflect impaired mucosal immune function, chronic stress, or selective IgA deficiency, and has been associated with increased susceptibility to enteric infection and dysbiosis. Elevated sIgA can accompany active mucosal immune responses to infection or inflammation.

Beta-glucuronidase is a bacterial enzyme that cleaves glucuronide conjugates in the intestinal lumen, reversing phase-II hepatic detoxification. Deconjugated metabolites, including oestrogens and xenobiotics, become available for reabsorption, which can increase systemic exposure.

Elevated faecal beta-glucuronidase activity has been linked to increased oestrogen recirculation and, in observational studies, to higher risk of hormone-dependent conditions. It is also a marker of dysbiosis, as certain bacterial taxa produce the enzyme in abundance.

Pancreatic elastase-1 is a proteolytic enzyme synthesised by the pancreatic acinar cells and secreted into the duodenum. Because it is not degraded during intestinal transit and its faecal concentration correlates with pancreatic output, it serves as a non-invasive marker of exocrine pancreatic function.

Low faecal elastase-1 indicates exocrine pancreatic insufficiency, which may be secondary to chronic pancreatitis, cystic fibrosis, pancreatic cancer, or severe coeliac disease. It is used to guide pancreatic enzyme replacement therapy and to differentiate malabsorption aetiologies.

Short-chain fatty acids — principally acetate, propionate, and butyrate — are the end products of bacterial fermentation of dietary fibre and resistant starch in the colon. Butyrate is the primary energy source for colonocytes and exerts anti-inflammatory and barrier-protective effects; propionate and acetate enter systemic circulation and influence hepatic and peripheral metabolism.

Low faecal SCFA, particularly butyrate, may reflect reduced fibre intake, diminished saccharolytic bacterial populations, or rapid colonic transit. The SCFA profile is used to assess colonic fermentation capacity and to guide dietary and prebiotic interventions, though its clinical validation is still evolving.

Steatocrit is a semi-quantitative measure of faecal fat, reflecting the proportion of lipid in stool. It serves as a screening tool for fat malabsorption when a formal 72-hour faecal-fat collection is impractical. Elevated steatocrit indicates maldigestion (pancreatic insufficiency) or malabsorption (small-bowel disease, bile-salt deficiency).

Elevated faecal fat points to exocrine pancreatic insufficiency, coeliac disease, small-intestinal bacterial overgrowth, bile-acid malabsorption, or mucosal disease. It should be correlated with pancreatic elastase-1 and clinical history to localise the defect.

Faecal occult blood tests detect haemoglobin or haem-derived products in stool, indicating gastrointestinal bleeding that may not be visible. Immunochemical methods (FIT) are specific for human haemoglobin and do not cross-react with dietary sources or upper-GI bleed unless transit is sufficiently slow.

A positive result requires investigation to exclude colorectal neoplasia, inflammatory bowel disease, polyps, diverticulosis, angiodysplasia, or upper-GI sources if transit is delayed. It is a screening tool for colorectal cancer in average-risk populations and a triage marker in symptomatic patients.

Microbial diversity indices summarise the number of distinct taxa (richness) and the evenness of their distribution (Shannon or Simpson indices) in a stool sample. High diversity is thought to confer functional redundancy and resilience, while low diversity has been associated with dysbiosis, antibiotic exposure, and metabolic and inflammatory disease.

Reduced diversity is a non-specific marker of dysbiosis and has been documented in irritable bowel syndrome, inflammatory bowel disease, obesity, and type 2 diabetes. It is used to guide dietary diversification, prebiotic and probiotic interventions, and to monitor recovery after antibiotic therapy.

Multiplex PCR assays detect DNA or RNA of bacterial, viral, and parasitic enteric pathogens, including Salmonella, Shigella, Campylobacter, toxigenic C. difficile, Giardia, Cryptosporidium, and enteric viruses. The assays are highly sensitive and specific, though detection does not always distinguish active infection from carriage or recent resolved infection.

A detected pathogen in the context of diarrhoea, abdominal pain, or systemic symptoms supports an infectious aetiology and guides antimicrobial or supportive therapy. Asymptomatic detection may reflect colonisation or post-infectious carriage and should be interpreted with clinical judgement.

Zonulin is a protein that modulates tight junctions between intestinal epithelial cells. Elevated zonulin in serum or stool is proposed as a marker of increased intestinal permeability, though assay specificity and the clinical relevance of zonulin as a standalone marker remain contested in mainstream gastroenterology.

Elevated faecal zonulin is interpreted in functional and integrative medicine as a marker of 'leaky gut' and has been associated with coeliac disease, type 1 diabetes, and inflammatory bowel disease in research settings. Its use for therapeutic decision-making is exploratory.

Next-generation sequencing of the 16S rRNA gene or shotgun metagenomics quantifies the relative abundance of bacterial phyla (Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria), families, genera, and sometimes species in stool. The profile reflects colonic microbial community structure, which is influenced by diet, antibiotics, host genetics, and disease.

Specific taxa have been associated with health (e.g. Faecalibacterium, Akkermansia, Bifidobacterium) or dysbiosis (e.g. elevated Proteobacteria, reduced Firmicutes:Bacteroidetes ratio in obesity). The clinical utility of single-taxon abundance is limited by inter-individual variation and the functional redundancy of the microbiome; interpretation should focus on patterns rather than isolated taxa.