Add-On: Fecal SIgA
The Fecal SIgA test quantifies secretory immunoglobulin A in stool, the intestinal mucosa's principal humoral defence. It is ordered as an add-on in functional gastroenterology to assess mucosal immune competence and barrier integrity, with low values interpreted as impaired defence and elevated values as active immune response, though thresholds are method-specific and not diagnostically…
1
Biomarkers
Stool
Sample
7–14 business days
Turnaround
No
Fasting
What is the Fecal SIgA test?
The Fecal SIgA test quantifies secretory immunoglobulin A in stool, the intestinal mucosa's principal humoral defence molecule. It is ordered as an add-on to comprehensive stool panels in functional and integrative gastroenterology to assess mucosal immune function and barrier integrity when practitioners suspect compromised intestinal defence, chronic dysbiosis, or immune dysregulation. Fecal SIgA is not a first-line diagnostic marker in conventional gastroenterology but is used in functional practice to characterise the mucosal immune environment and to guide interventions aimed at restoring barrier health, modulating microbial balance, and supporting the mucosal immune system. Interpretation depends on laboratory-specific intervals, clinical context, and integration with microbiome, inflammatory, and digestive markers.
What does the Fecal SIgA test measure?
Secretory IgA is the predominant antibody class in mucosal secretions and the primary humoral defence at the intestinal epithelium. It is produced by plasma cells in the lamina propria, transported across the epithelium bound to the polymeric immunoglobulin receptor, and released into the lumen as a dimeric molecule with a secretory component. SIgA binds and neutralises pathogens, toxins, and dietary antigens, blocks microbial adherence, and modulates the commensal microbiota without triggering inflammation. Faecal SIgA concentration reflects the functional output of the gut-associated lymphoid tissue and the mucosal barrier's immunological tone.
Fecal SIgA is used in functional and integrative gastroenterology as a marker of mucosal immune competence and intestinal barrier integrity. Low concentrations are interpreted as impaired mucosal defence, which may correlate with dysbiosis, chronic infection, or immune exhaustion, though the threshold for clinically significant suppression is not standardised. Elevated SIgA may reflect an active mucosal immune response to pathogens, inflammation, or antigenic challenge. Because the marker is method-dependent and interpretive thresholds are not universally defined, results are used to inform a functional assessment rather than to diagnose or exclude specific disease.
Why is the Fecal SIgA test ordered?
- Assessment of suspected mucosal immune compromise in patients with recurrent gastrointestinal infections, chronic diarrhoea, or dysbiosis not explained by standard diagnostics
- Evaluation of intestinal barrier integrity in patients with food sensitivities, chronic inflammatory symptoms, or suspected 'leaky gut' in a functional-medicine framework
- Monitoring mucosal immune response in chronic gut inflammation, post-infectious irritable bowel syndrome, or small intestinal bacterial overgrowth
- Investigation of immune dysregulation in patients with autoimmune conditions or systemic inflammation and gastrointestinal symptoms
- Functional assessment alongside comprehensive stool analysis in patients with unexplained fatigue, malabsorption, or refractory digestive complaints
- Follow-up of interventions targeting gut barrier repair, probiotic or prebiotic therapy, or immune modulation in integrative protocols
Sample collection and turnaround
Sample type
Stool
Fasting required
No
Collection method
At-home collection kit
Turnaround
7–14 business days
Collection notes
Patient collects a stool sample at home using the kit provided by Genova Diagnostics, following the laboratory's instructions for specimen collection and handling. The sample should be frozen promptly if shipping is delayed. Avoid collection during menses or if there is visible blood or urine contamination. Note any recent antibiotic, probiotic, or immunosuppressive therapy on the requisition.
Specimen requirements
Stool specimen collected in the laboratory-provided container; refer to Genova's collection instructions for volume and preservative requirements. Freeze if shipment will exceed 24 hours. Ship with cold packs per the kit instructions.
What can affect Fecal SIgA results?
Diarrhoea dilutes faecal SIgA concentration and may produce spuriously low results, while hard or dehydrated stool may concentrate it; reporting per gram of stool partially controls for this but interpretation should account for stool form.
NSAIDs can injure the mucosa and alter secretory function; corticosteroids suppress mucosal immunity and may reduce SIgA production or alter its clearance.
Conditions or medications that impair B-cell function or plasma-cell numbers (chemotherapy, selective IgA deficiency, severe combined immunodeficiency) reduce faecal SIgA output.
Bacterial or fungal proteases in the lumen can degrade secreted IgA, lowering measured concentrations and potentially masking an adequate mucosal response.
Certain probiotics and prebiotics have been shown to stimulate SIgA secretion; interpretation of a result obtained during active supplementation should account for this effect.
SIgA stability in stool depends on storage temperature and time; specimens should be frozen promptly if delayed shipping is anticipated to prevent degradation.
What do Fecal SIgA results mean?
Elevated
Elevated faecal SIgA may reflect an active mucosal immune response to infection, parasitic infestation, inflammatory bowel disease, coeliac disease, or chronic antigenic stimulation. It can also be seen transiently with probiotic therapy or acute gastroenteritis. High values are not inherently pathological but prompt correlation with clinical symptoms, inflammatory markers, and microbial findings.
Normal
A result within the reference range suggests adequate mucosal IgA secretion under the conditions of specimen collection. Because reference intervals are method-specific and functional thresholds are not validated, a normal value does not exclude barrier dysfunction or immune dysregulation and should be read with the rest of the stool panel and clinical context.
Reduced
Low faecal SIgA is interpreted in functional practice as impaired mucosal immune defence, potentially associated with dysbiosis, chronic stress, malnutrition, immunosuppression, or immune exhaustion. Practitioners may investigate primary or secondary immunodeficiency, proteolytic microbial overgrowth, or barrier compromise, though standardised thresholds for clinically significant suppression are not established.
Note: Faecal SIgA is method-dependent and influenced by stool consistency, microbial proteases, medications, and recent supplementation. It is a functional marker rather than a diagnostic test, and thresholds for abnormality are not standardised across laboratories or clinical guidelines. Results inform an integrative assessment and are not interchangeable with serum IgA.
Frequently asked questions
Secretory IgA is the dominant antibody at mucosal surfaces, including the gut, where it neutralises pathogens and toxins and modulates the microbiota without triggering inflammation. Measuring it in stool provides a functional assessment of mucosal immune output and barrier defence.
How to access the Fecal SIgA test
The Fecal SIgA reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Woof JM, Kerr MA. The function of immunoglobulin A in immunity. J Pathol. (2006)
- Brandtzaeg P. Secretory IgA: designed for anti-microbial defense. Front Immunol. (2013)
- Gleeson M, et al. The anti-inflammatory effects of exercise: mechanisms and implications for the prevention and treatment of disease. Nat Rev Immunol. (2011)
- Macpherson AJ, McCoy KD, et al. The mucosal firewalls against commensal intestinal microbes. Semin Immunopathol. (2009)
- Corthésy B. Multi-faceted functions of secretory IgA at mucosal surfaces. Front Immunol. (2013)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.