Measurement · Poorly validated
Faecal secretory IgA: what it measures, and what it does not
The concentration of secretory IgA in the portion of stool that was sampled and assayed.
What it measures
The concentration of secretory IgA in the portion of stool that was sampled and assayed.
Compartment sampled: Stool, from the portion of a single bowel movement that was sampled.
Assay principle: Immunoassay of secretory IgA in a stool extract, normalised to sample weight or extract volume.
What it does not measure
It does not measure mucosal immune competence, immune 'exhaustion', or antigen-specific responses, and it does not support a high/low interpretation of immune activity.
Sources of variance
Each of the following can change the reported number without any change in the underlying biology.
- Stool consistency and water content
- Sampling site within the stool
- Transit time
- Assay platform differences
The common misinterpretation
Reading a low value as a 'depleted' mucosal immune system and a high value as 'immune activation'.
What one result cannot establish
- Mucosal immune competence, or any state described as immune 'exhaustion'.
- Antigen-specific mucosal responses.
- That a value outside a vendor range corresponds to a biological abnormality.
What repeated results would mean
- A series taken under similar stool consistency and transit conditions describes analytical and day-to-day variability.
- Repetition does not add construct validity: repeating a poorly validated measure produces a more precise estimate of the same unvalidated quantity.
How BiomeLogic uses it
Treated as a weak proxy. No interpretation is built on a single value.
Validity class recorded in the BiomeLogic measurement registry: Poorly validated (BL-MEAS-0003).
Evidence boundary matrix
The boundary of this measurement, stated as propositions rather than as a verdict on any result.
| Proposition | Population / model | Evidence class | What it supports | What it does NOT support | Sources |
|---|---|---|---|---|---|
| Faecal secretory IgA reports the quantity described above. | Stool, from the portion of a single bowel movement that was sampled. | Poorly validated | The concentration of secretory IgA in the portion of stool that was sampled and assayed. | It does not measure mucosal immune competence, immune 'exhaustion', or antigen-specific responses, and it does not support a high/low interpretation of immune activity. |
|
| A single faecal secretory iga value describes the person's underlying state. | Stool, from the portion of a single bowel movement that was sampled. | Not supported by the measurement | A description of the sample that was assayed. | Mucosal immune competence, or any state described as immune 'exhaustion'. Antigen-specific mucosal responses. That a value outside a vendor range corresponds to a biological abnormality. |
|
Question answered on this page
What does faecal secretory iga actually measure?
Short answer
The concentration of secretory IgA in the portion of stool that was sampled and assayed. It does not measure mucosal immune competence, immune 'exhaustion', or antigen-specific responses, and it does not support a high/low interpretation of immune activity. In the BiomeLogic measurement registry it is recorded as: poorly validated.
What is established
The concentration of secretory IgA in the portion of stool that was sampled and assayed.
Population / model: Stool, from the portion of a single bowel movement that was sampled.. Sources: BL-REF-0010 (verification pending).
What human evidence shows
No direct human evidence is claimed for this question.
What experimental / non-human evidence shows
No animal or in-vitro evidence is claimed for this question.
Alternative explanations
The measurement is read as a proxy for the biology of interest
Reading a low value as a 'depleted' mucosal immune system and a high value as 'immune activation'.
The measurement is read as a description of the sample assayed
This reading stays inside what the assay detects. It does not measure mucosal immune competence, immune 'exhaustion', or antigen-specific responses, and it does not support a high/low interpretation of immune activity.
What is not yet known
- Mucosal immune competence, or any state described as immune 'exhaustion'.
- Antigen-specific mucosal responses.
- That a value outside a vendor range corresponds to a biological abnormality.
What evidence would discriminate these explanations
- A series taken under similar stool consistency and transit conditions describes analytical and day-to-day variability.
- Repetition does not add construct validity: repeating a poorly validated measure produces a more precise estimate of the same unvalidated quantity.
Sources
0 of 1 reference(s) have completed owner verification. Records awaiting verification are listed for transparency and are not presented as confirmed evidence.
- BL-REF-0010verification pending
Multiple (mucosal immunology reviews) (2018). Secretory IgA and the regulation of intestinal microbial communities. Peer-reviewed review literature.
Scope: Establishes sIgA's role in mucosal defence and community shaping. Does not establish that a single faecal sIgA value reflects mucosal immune competence.
Status: generic placeholder — not a bibliographic record
What this page does NOT establish
- Any interpretation of an individual reader's result.
- A reference range, cut-off, or decision threshold.
- That this test should or should not be performed.
Educational systems-biology material. Not medical advice, not a diagnosis, and not a treatment recommendation. No dosing, protocol, or personal lab interpretation is given here.
Page provenance
- Canonical title
- Faecal secretory IgA: what it measures and what it does not
- Canonical URL
- https://biomelogic.net/measurements/faecal-secretory-iga
- Author
- Mohammed Attallah — Systems Biology Consultant
- Publisher
- BiomeLogic
- Version
- 1.0
- First published
- n.d.
- Last substantive revision
- n.d.
- Last evidence review
- n.d.
- Evidence classes present
- Assay validation literature; Clinical consensus / methodology; BiomeLogic editorial classification
- Publication-eligible references
- 0 of 1
Scope
A vendor-independent account of faecal secretory iga: the quantity detected, the compartment sampled, the sources of variance, the inference limits of one result, and the reading the measurement does not support.
What this page does not establish
- Interpretation of a reader's own result.
- Thresholds, ranges, or cut-offs.
- A recommendation to order, repeat, or avoid this test.
Cite this page
Mohammed Attallah (n.d.). Faecal secretory IgA: what it measures and what it does not (Version 1.0). BiomeLogic. https://biomelogic.net/measurements/faecal-secretory-iga
External citation packet
- Stable URL
- https://biomelogic.net/measurements/faecal-secretory-iga
- Scope
- What faecal secretory iga physically detects, and the inferences it cannot support.
- Established vs BiomeLogic inference
- Established: The concentration of secretory IgA in the portion of stool that was sampled and assayed. — BiomeLogic inference: that poorly validated is the appropriate validity class for this measure — a BiomeLogic editorial classification, not a published grading
- Key references
- BL-REF-0010 (verification pending)
- Exact citation text
- Mohammed Attallah (n.d.). Faecal secretory IgA: what it measures and what it does not (Version 1.0). BiomeLogic. https://biomelogic.net/measurements/faecal-secretory-iga