Key facts
- What it is: the primary antibody of mucosal (gut) immunity.
- On the GI-MAP: reported as an intestinal-health marker.
- Why it matters: reflects the activity of the gut's immune barrier.
- Method: measured by immunoassay (ELISA).
Secretory IgA (sIgA) is the most abundant antibody at mucosal surfaces and the front line of the gut's immune defence. It coats and neutralises microbes and toxins in a process called immune exclusion, keeping them from attaching to the intestinal lining. The GI-MAP (Gastrointestinal Microbial Assay Plus) reports total sIgA as an intestinal-health marker.
What secretory IgA does
Secretory IgA is purpose-built for anti-microbial defence at the mucosa: it binds pathogens and their toxins, shapes which microbes colonise the gut, and does so without triggering inflammation (PMID: 23964273). Healthy sIgA is part of a well-functioning gut barrier.
Reading high or low sIgA
A very high sIgA can reflect an active mucosal immune response to something the immune system is reacting to, while a low sIgA may reflect a weakened or depleted mucosal barrier. Neither finding is a diagnosis; both are interpreted alongside the microbial findings on the GI-MAP and the person's history by a qualified practitioner.
Result explainer
My sIgA came back high, low, or in range
Tap what your report says.
High secretory IgA
An elevated value can reflect an active mucosal immune response — the gut immune system reacting to something. What it does not do is name what that something is.
The useful next step is reading it against the microbial findings on the same panel and your symptoms, which is the job of the practitioner interpreting it. A high value on its own does not identify a cause or point to a protocol.
Low secretory IgA
A low value may reflect a weakened or depleted mucosal barrier. There is also a specific medical explanation worth knowing about: selective IgA deficiency is a recognised immune condition in which the body produces little or no IgA, and someone with it would show low sIgA for that reason rather than because of anything happening in their gut.
If your sIgA is low and no explanation is apparent, that is a question for a clinician who can assess you — not something to address with supplements on the strength of a stool marker.
Within the reference range
A value inside the range is unremarkable for this marker. It is not evidence that the rest of the panel is unremarkable, and it does not rule out conditions the panel does not test for.
Two limits that apply to all three. Fecal sIgA reference ranges are not standardised across laboratories, so a value is not directly comparable between labs or methods — comparisons over time are most meaningful using the same laboratory each time. And it is a supportive marker, not a diagnostic test: no condition is diagnosed by a stool sIgA value.
What high secretory IgA does not tell you
If you have arrived here because your report flagged sIgA as high or low, this is the part worth reading. A flagged sIgA value tells you the measured quantity sat outside the reference range used by the laboratory. It does not name a cause, and it does not identify what your immune system may be responding to.
Two limitations deserve stating plainly, because they change how much weight the number should carry:
- Reference ranges are not standardised across laboratories. Fecal sIgA is measured by immunoassay, and different assays and different laboratories use different ranges. A value called “high” on one report is not directly comparable to a number from a different lab or a different method. Comparisons over time are most meaningful when the same laboratory and method are used each time.
- It is a supportive marker, not a diagnostic test. No condition is diagnosed by a stool sIgA value. It is one input among the 85+ markers on the panel, and it earns its keep as context for the microbial findings rather than as a standalone result.
There is also a specific medical situation worth knowing about: selective IgA deficiency is a recognised immune condition in which the body produces little or no IgA. Someone with it would be expected to show low sIgA for that reason rather than because of anything happening in their gut. If your sIgA is low and no explanation is apparent, that is a question for a clinician who can assess you, not something to address with supplements on the strength of a stool marker.
What to actually do with the result
Bring it to the practitioner interpreting your panel and ask what it means in combination with the rest of your results — the microbial findings, calprotectin, and your symptoms and history. An sIgA value read on its own, without that context, is close to uninterpretable, and any protocol built on it alone is built on very little.
See how GI-MAP results are reported for how reference ranges and flagged values work across the panel.
The GI-MAP™ reports this and 85+ other markers from one at-home sample.
Order Your GI-MAP™ Test → See pricingReferences
- Brandtzaeg P. Secretory IgA: designed for anti-microbial defense. Front Immunol. 2013;4:222. PMID: 23964273.