Celiac Index

The antibody-testing layer of celiac diagnosis: useful for screening, useful for monitoring, but only interpretable in the context of ongoing gluten exposure.

Serology in celiac disease refers to blood tests that detect the antibody response generated during active disease. In practice, serology is the first diagnostic layer because it is cheap, scalable, and much less invasive than endoscopy and biopsy.

Core Tests

TTG IgA

The main first-line test.

Best screening test in routine practice
Correlates broadly with disease activity
Falls after starting a gluten-free diet
Can be falsely reassuring if the patient is already restricting gluten

EMA

Endomysial antibody is highly specific and is most useful as a confirmatory test when the diagnostic picture is close but not fully settled.

DGP

Deamidated gliadin peptide testing is especially useful when standard IgA-based testing is unreliable or when a more focused gluten-peptide assay is needed.

The IgA Problem

A central caveat in celiac serology is IgA deficiency. If a patient does not produce enough IgA, then IgA-based tests can appear negative even in real disease.

That is why the serology layer is really:

TTG IgA as the default
total IgA or explicit assessment for IgA deficiency
IgG-based alternatives when IgA deficiency is present

What Serology Can and Cannot Do

Good at

Screening symptomatic patients
Triaging who should proceed to biopsy
Monitoring broad response to a gluten-free diet
Supporting paediatric no-biopsy pathways in tightly defined cases

Not good at

Diagnosing someone already off gluten
Fully replacing histology in most adults
Distinguishing celiac from every neighboring condition on its own

Relationship to Gluten Challenge

Serology depends on active immune stimulation. If gluten has already been removed, antibodies can normalize. That is why a gluten challenge may be needed before testing.

Relationship to Mechanism

Serology is a downstream readout of the deeper mechanism:

gliadin exposure starts the process
tissue-transglutaminase modifies peptides and becomes the autoantigen
autoantibodies become detectable in blood

So serology is not just a test battery; it is a measurable surface expression of the core autoimmune pathway.

Source Basis

Compiled from the current wiki corpus, especially diagnosis, ttg-iga-test, iga-and-iga-deficiency, and autoantibodies-celiac.