This page explains what each test measures, the order the tests are usually run in, and where the decision passes to a clinician. It is educational and not medical advice.
Celiac disease is an immune reaction to gluten, the protein in wheat, barley and rye, that damages the lining of the small intestine in genetically susceptible people 1. The damage is not an allergy and not a sensitivity in the loose sense of the word. It is an antibody-driven process against the body's own tissue, triggered by a food protein, and it keeps going as long as gluten keeps arriving.
Research suggests that celiac disease affects around 1% of people in many populations and that a large share of cases remain unrecognised 1. Presentation is broad, running from classic digestive symptoms to iron deficiency, fatigue, poor growth in children, bone or skin findings, or almost nothing noticeable 2.
The order of testing matters for one mechanical reason. Blood tests look for the immune response to gluten, not for gluten itself, so the signal depends on ongoing exposure. Guidelines are explicit that serologic testing should be done while the person is still eating a gluten-containing diet 3.
The practical sequence is straightforward. Raise the question with a clinician, run the blood work while eating normally, and let the results guide what comes next. Changing the diet first is the most common way a clear answer gets lost, and rebuilding that answer later takes weeks of deliberate gluten reintroduction under supervision.
Total IgA (Immunoglobulin A) measures the overall amount of immunoglobulin A, one of the main antibody classes, circulating in blood. It belongs in celiac testing for one reason. The first-line celiac test measures an IgA-class antibody, so in people who produce very little IgA overall, that test can read negative even when intestinal damage is present.
Guidelines therefore recommend measuring total IgA alongside the celiac antibody test, or switching to IgG-based antibody tests when IgA is low 3. Selective IgA deficiency is more common in people with celiac disease than in the general population, which is exactly why the pairing exists 3.
The first blood test is tissue transglutaminase IgA, written tTG-IgA on most lab reports. Tissue transglutaminase is an enzyme in the gut wall that chemically modifies gluten fragments, and in celiac disease the immune system produces antibodies against that enzyme. Measuring those antibodies is an indirect read on the immune process happening in the small intestine.
Guidelines name tTG-IgA the preferred initial test in people on a gluten-containing diet, ordered together with total IgA 3. Updated adult guidance keeps that pairing as the entry point to the diagnostic pathway 5. Studies indicate that modern tTG-IgA assays combine high sensitivity with high specificity, which is why a single well-timed test carries so much weight in the workup 4.
Practically, this is one standard venous blood draw. Fasting is not normally required for the antibody tests themselves, although other markers ordered at the same visit may have their own instructions. Results usually come back within a few days, reported against the laboratory's own cut-off rather than a universal number.
What the test gives you is a signal, not a verdict. A raised tTG-IgA points toward an immune response consistent with celiac disease and triggers the next step. A normal tTG-IgA in someone eating gluten with normal total IgA makes celiac disease considerably less likely, though it does not close every question if symptoms persist. Either way, the interpretation belongs with a clinician who can see the whole picture.
Because antibody levels fall once the trigger is removed. When gluten comes out of the diet, the immune response quietens and tTG-IgA levels decline, which is useful after a confirmed diagnosis but destructive before one. Guidelines state plainly that testing should be performed while gluten is still being eaten 3.
This is the single most common reason a celiac workup ends in ambiguity. Someone feels better without bread, removes it for two months, then asks for a test, and the blood work comes back clean. That result cannot distinguish between a person who never had celiac disease and a person whose antibodies have already subsided.
In people already avoiding gluten, the route back is a supervised gluten challenge, where gluten is deliberately reintroduced for a defined period before retesting 6. Updated adult guidance describes the challenge as a clinician-directed step, with the amount and duration decided case by case and symptoms monitored along the way 5. This page gives no amounts and no schedule. That decision sits with the clinician ordering the test, who weighs how uncomfortable the reintroduction is likely to be against how much the answer is worth.
If a gluten challenge is genuinely not tolerable, genetic testing becomes more useful, because it can make celiac disease very unlikely without requiring any gluten exposure at all.
Several antibody tests exist, each with a defined role rather than being interchangeable options. Endomysial antibody (EMA) IgA is the main confirmatory test, and studies suggest it carries very high specificity, although it is read by microscopy and is more operator dependent than automated assays 4. Deamidated gliadin peptide (DGP) IgG and tTG-IgG step in when total IgA is low, since they do not depend on IgA production 3. Older anti-gliadin antibody tests have been superseded and guidelines no longer recommend them for initial testing 3.
| Test | What it measures | Usual role |
|---|---|---|
| tTG-IgA | IgA antibodies against tissue transglutaminase | First-line test in people eating gluten 3 |
| Total IgA | Overall immunoglobulin A level | Run with tTG-IgA to detect IgA deficiency 3 |
| EMA-IgA | IgA antibodies against endomysium | Confirmatory, highly specific, microscopy based 4 |
| tTG-IgG | IgG antibodies against tissue transglutaminase | Used when total IgA is low 3 |
| DGP-IgG | IgG antibodies against deamidated gliadin peptides | Used when total IgA is low 3 |
| HLA-DQ2 / DQ8 | Genetic susceptibility | Helps rule out rather than confirm 3 |
Ordering everything at once is rarely the efficient move. The standard approach starts narrow, with tTG-IgA and total IgA, and widens only when those two results raise a specific question.
Celiac antibody results are reported against each laboratory's own cut-off, not against a single universal number. Units and calibration differ between manufacturers, so a titre from one laboratory is not directly comparable with a titre from another, and serial results are most meaningful when run on the same assay 4. This is why reports describe values as multiples of the upper limit of normal rather than quoting a figure that travels between labs.
Total IgA is different, because it is a straightforward concentration measurement with established reference ranges.
| Measure | Typical lab reference range (adults) | FitScript optimal range |
|---|---|---|
| Total IgA | 47 to 400 mg/dL | 70 to 400 mg/dL |
Reference ranges vary by laboratory, age and sex, and children have their own age-specific ranges. FitScript's optimal range is an optimization target, not a diagnostic cut-off, and a result inside or outside it is not a diagnosis of anything on its own.
For celiac testing specifically, the number that changes the interpretation is a very low total IgA, because that is the situation in which an IgA-based antibody test loses reliability and IgG-based testing is used instead 3. A total IgA sitting modestly below the reference range is a separate conversation with a clinician, who can decide whether it reflects a real deficiency or simply where that person sits.
Each result category sends the workup in a different direction, and none of them is a diagnosis by itself.
A clearly raised tTG-IgA in someone eating gluten reflects an immune response consistent with celiac disease and is the trigger for specialist referral. The higher the value relative to the laboratory's upper limit of normal, the more weight it carries, and current adult guidance builds its pathway around that gradient 5.
A borderline or weakly raised value is the harder situation. Low-level elevations can reflect early or patchy intestinal changes, other immune conditions, or assay behaviour near the cut-off, and guidance recognises that these cases need careful follow-up rather than a quick label 8. The usual next step is confirmatory antibody testing, repeat measurement, or specialist assessment.
A negative tTG-IgA with a normal total IgA, in someone genuinely eating gluten, makes celiac disease substantially less likely. It does not explain ongoing symptoms, and it does not rule out every presentation, since seronegative cases exist and are recognised in current guidance 8.
The reading frame to keep is observation, then meaning, then next step. The observation is a number. The meaning is a probability, shaped by diet, total IgA and symptoms. The next step always belongs to a clinician, and no result on this page should be read as telling anyone what they have.
A positive result normally leads to referral to a gastroenterologist rather than to a diet change. The confirmatory step in most adults is an upper endoscopy with multiple biopsies of the duodenum, examined for the characteristic changes in the intestinal lining, and guidelines stress that this is done while gluten is still being eaten 3.
That requirement surprises people. It feels counterintuitive to keep eating the thing suspected of causing harm, but the biopsy looks for active damage, and that damage begins to repair once gluten is withdrawn. Removing gluten between the blood test and the endoscopy can leave both results inconclusive.
Adult guidance updated in 2025 also describes a route to diagnosis without biopsy for selected adults, when tTG-IgA is very high, at or above ten times the laboratory's upper limit of normal, with confirmation on a second antibody test and assessment by a specialist 5. Work on refining both the biopsy and non-biopsy routes continues to shape how these pathways are applied in practice 8.
Whichever route is used, the decision is the specialist's. Diet, follow-up and any further investigation are decided after the diagnosis is settled, by the clinician managing the case, and that conversation is worth having before changing anything.
Genetic testing is useful mainly in the negative direction. Celiac disease develops almost exclusively in people carrying the HLA-DQ2 or HLA-DQ8 genetic types, so the absence of both makes the condition very unlikely and can effectively close the question 3.
The reverse is not true. A large share of the general population carries DQ2 or DQ8 and never develops celiac disease, so a positive genetic result confirms susceptibility rather than disease 1. Using genetics as a first-line test would generate far more false alarms than answers.
Where genetic testing earns its place is in specific situations. It helps when someone has already removed gluten and cannot face a challenge, because the genes do not change with diet. It helps in first-degree relatives who want to know whether ongoing surveillance is worth the effort. It also helps when antibody results and biopsy findings disagree and a specialist needs another angle.
The test itself is a simple blood or cheek-swab sample with no dietary preparation. The interpretation still needs a clinician, because the usefulness of the answer depends entirely on which question it was ordered to settle.
Testing is usually considered in people with ongoing digestive symptoms, unexplained nutrient deficiencies, or a family history of celiac disease. Chronic diarrhoea, bloating, abdominal pain, unintended weight change and persistent fatigue are the familiar prompts, but the condition presents in ways that have nothing to do with the gut 2.
Unexplained iron deficiency anaemia is one of the most recognised non-digestive presentations and is associated with undiagnosed celiac disease in a meaningful minority of cases 2. Low bone density, raised liver enzymes, recurrent mouth ulcers, certain skin rashes and poor growth in children are other routes by which the question gets asked 1.
First-degree relatives of someone with confirmed celiac disease carry a substantially higher risk than the general population, and guidelines support testing them when symptoms or supporting findings are present 3. Testing is also commonly considered in people with certain other autoimmune conditions, where the two cluster together more often than chance would predict 1.
None of this means everyone needs the panel. It means that if the pattern fits, the test is cheap, low-burden and far more informative than an experimental diet change, provided it happens in the right order.
Four things account for most of the confusion.
The first is prior gluten avoidance, which lowers antibody levels and is the leading cause of a falsely reassuring result 3. The second is low total IgA, which undermines the IgA-based test and calls for IgG-based alternatives 3.
The third is assay variation. Different manufacturers calibrate differently, cut-offs are not uniform, and values measured near the threshold carry more uncertainty than a report's single number suggests 4. Comparing a result from one laboratory with a result from another, or treating a small change in titre as meaningful, invites misreading.
The fourth is that the intestinal findings themselves are not unique to celiac disease. Other conditions can produce similar changes in the small intestine, and seronegative presentations exist where antibodies stay normal despite genuine disease, which is why specialist assessment rather than any single result settles difficult cases 8.
The reasonable response to an unclear result is not to guess. It is to take the full set of numbers, the symptom history and the diet history back to a clinician who can decide whether to repeat, extend or redirect the testing.
The starting point is the same, with tTG-IgA and total IgA drawn while gluten is still in the diet, but paediatric pathways diverge after that. Children are assessed against age-specific reference ranges, and a paediatric gastroenterologist, not an adult service, makes the decisions about confirmation.
Non-biopsy diagnosis has been established in paediatric practice for longer than in adults, and the criteria used in children have shaped how the adult pathways were later developed 8.
Growth and development add urgency that adults do not have. Faltering growth, delayed puberty or persistent iron deficiency in a child are reasons to ask the question early rather than wait and watch 1.
One rule carries across both groups without exception. Do not remove gluten from a child's diet to see whether symptoms improve before testing has been arranged. It makes the subsequent workup harder for everyone, including the child.
A celiac workup rarely sits alone, because the downstream effects of intestinal damage show up in other blood work. Guidelines support checking for nutritional deficiencies around the time of diagnosis, since absorption across the damaged section of small intestine is where the real-world consequences appear 3.
The markers usually considered alongside the antibody tests include a full blood count, ferritin and iron studies, vitamin B12, folate, vitamin D, calcium and liver enzymes. Each one answers a different question about how long the process may have been running and what it has cost. Raised liver enzymes and reduced bone density are both recognised findings in people with celiac disease 2.
None of these confirm or exclude celiac disease. They describe the consequences, and they give the clinician a baseline to compare against later.
FitScript tests 150+ biomarkers per year, Atlas interprets the results in context, and any clinical decision is made by a licensed provider after reviewing the member. Interpretation of a celiac workup specifically belongs with the clinician who ordered it.
Follow-up usually involves repeating the antibody test over time, because levels fall as the immune trigger is removed. Research suggests that declining tTG-IgA reflects reduced gluten exposure reasonably well but correlates imperfectly with healing of the intestinal lining, so a normal antibody level does not guarantee that the gut has fully recovered 7.
That gap matters. Someone can have antibodies back inside the reference range while biopsies still show incomplete recovery, which is why some specialists arrange repeat endoscopy in selected cases rather than relying on blood work alone 7.
The nutrient markers checked at diagnosis are usually rechecked as well, to see whether deficiencies are correcting. Rising antibody levels after a period of decline generally prompt a review of dietary gluten exposure, often with dietetic input, before anything else is considered.
The cadence of follow-up, and what counts as adequate progress, is set by the managing clinician. Nothing here replaces that plan.
It is worth raising the question before you change your diet, not after. If digestive symptoms have persisted for weeks, if iron deficiency keeps returning without explanation, if a first-degree relative has confirmed celiac disease, or if fatigue and unexplained weight change have no obvious cause, those are reasons to ask about testing.
Get in touch with a clinician promptly if symptoms are severe, if weight is dropping without intention, if there is blood in the stool, or if a child's growth has slowed. Those situations need assessment on their own terms, independent of any antibody result.
A suboptimal or unexpected result is also a reason to make contact rather than to interpret it alone. That includes a low total IgA, a borderline antibody value, or a negative result that does not fit a convincing symptom picture. Discuss your results and any proposed next step with a clinician or licensed provider, who can weigh the full context and decide what, if anything, follows.
Yes. Celiac blood tests look for an immune response to gluten, so they are taken while gluten is still a normal part of meals. In people already avoiding gluten, a clinician decides whether to reintroduce it before testing and for how long. Do not restart gluten on your own after a long period without it.
Tissue transglutaminase IgA, written tTG-IgA, ordered together with total IgA. The two are run as a pair because the main test measures an IgA-class antibody, and someone who produces very little IgA overall can get a negative result that does not reflect what is happening in the small intestine.
No. A blood test does not diagnose celiac disease on its own. A raised antibody level signals that the immune system may be reacting to gluten, and a clinician decides the next step, which is often referral to a gastroenterologist for an upper endoscopy with small intestine biopsies.
A low total IgA means the standard IgA-based celiac test can read falsely negative. In that situation a clinician usually orders IgG-based antibody tests instead and interprets them alongside symptoms and other findings. The low total IgA itself is worth discussing with a clinician as a separate question.
Usually not. The antibody tests run on a standard venous blood sample and do not normally require fasting, although other markers ordered at the same visit might. Follow the instructions given by the ordering clinician or the laboratory, since panels differ in what they include.
A home or point-of-care kit can flag a possible antibody response, but it cannot replace a laboratory panel read alongside total IgA, and it cannot settle the diagnosis. Any positive or unclear home result is worth taking to a clinician, who decides what confirmatory testing is appropriate.
Not always. In some adults with very high antibody levels confirmed on a second test, a specialist may reach a diagnosis without endoscopy. In other cases a biopsy is the step that settles the question. A gastroenterologist makes that call, and any biopsy is done while gluten is still in the diet.
A negative result makes celiac disease less likely but does not explain ongoing symptoms, especially where gluten intake was low beforehand or total IgA is reduced. Take the symptoms back to a clinician, who can repeat or widen the testing and consider other explanations.
No. HLA-DQ2 and DQ8 testing is most useful the other way around. Without those genetic types, celiac disease becomes very unlikely. Many people carry them and never develop the condition, so a positive genetic result on its own confirms susceptibility rather than disease.