Celiac Disease
The one diagnosis where the order of events decides whether you can make it at all: test before the patient goes gluten-free, because a gluten-free diet normalizes both serology and histology within weeks and leaves you unable to confirm or exclude anything. Most patients present without diarrhea, the commonest reason treatment fails is hidden gluten rather than refractory disease, and the diagnosis obligates screening the family.
🔍 Overview
What It Is
Celiac disease is an immune-mediated enteropathy triggered by gluten in genetically susceptible people (essentially all carry HLA-DQ2 or DQ8). Gluten peptides deamidated by tissue transglutaminase drive a T-cell response that produces villous atrophy, crypt hyperplasia and intraepithelial lymphocytosis in the small bowel -which is why the disease is defined by malabsorption even when the presentation is not obviously intestinal. It affects roughly 1% of the population and remains substantially underdiagnosed.
How It Actually Presents
- Most adults do NOT present with classic diarrhea and steatorrhea. The textbook picture is now the minority, which is precisely why the diagnosis is missed.
- The commonest adult presentations are extraintestinal: iron deficiency anemia unresponsive to oral iron (often the only clue), fatigue, osteoporosis or unexplained fractures, transaminase elevation, infertility or recurrent miscarriage, neuropathy, and headache.
- GI symptoms when present may be bloating, flatulence, abdominal pain and weight change rather than diarrhea, and are frequently labeled irritable bowel syndrome for years.
- Dermatitis herpetiformis -intensely pruritic vesicles on extensor surfaces, elbows, knees and buttocks -is celiac disease of the skin and is diagnostic in its own right; these patients need the diet whether or not they have gut symptoms.
Who to Test
- Symptomatic: chronic diarrhea, unexplained weight loss, malabsorption, IBS-type symptoms not responding to standard care, and especially iron deficiency anemia without an obvious source.
- Associated conditions: type 1 diabetes, autoimmune thyroid disease, Down and Turner syndromes, IgA deficiency, autoimmune hepatitis, unexplained transaminitis, premature osteoporosis.
- First-degree relatives of a patient with confirmed celiac disease -risk is roughly ten-fold, and many are asymptomatic.
- Do not test the general population; test on symptoms, associated disease, or family history.
🧪 Diagnosis
Test BEFORE the gluten-free diet starts. This is the single most consequential rule in the topic. A gluten-free diet normalizes serology and heals the mucosa within weeks to months, so a patient who has already gone gluten-free cannot be confirmed or excluded -and they are left with a lifelong restrictive diet on no evidence, or a missed diagnosis with real complications. If the patient has already stopped gluten, the options are a formal gluten challenge (typically several weeks of adequate daily gluten before retesting, which many find intolerable) or HLA typing, which is useful only to exclude: a negative DQ2/DQ8 makes celiac disease essentially impossible, while a positive result is common in the general population and proves nothing.
Serology (on a gluten-containing diet)
- Tissue transglutaminase IgA (tTG-IgA) is the first-line test -high sensitivity and specificity, inexpensive, and the one to order when ordering only one.
- ⚠ Always order total IgA at the same time. Selective IgA deficiency is markedly more common in celiac disease than in the general population, and an IgA-deficient patient produces a falsely negative tTG-IgA. If IgA is low, switch to IgG-based testing (deamidated gliadin peptide IgG or tTG-IgG).
- Endomysial antibody (EMA) IgA is highly specific and used as a confirmatory test where the tTG is equivocal.
- Antibody titer correlates loosely with mucosal damage, and very high tTG levels (conventionally ≥ 10 times the upper limit of normal) support the diagnosis strongly -in children, a no-biopsy pathway exists on that basis with confirmatory EMA, but adults are generally still biopsied.
Biopsy
- Upper endoscopy with duodenal biopsies confirms the diagnosis in adults: take at least four biopsies from the distal duodenum plus one or two from the duodenal bulb, because the disease is patchy and inadequate sampling is a common cause of a falsely negative biopsy.
- Histology shows intraepithelial lymphocytosis, crypt hyperplasia and villous atrophy (graded by the Marsh classification).
- Villous atrophy is not specific to celiac disease -consider giardiasis, small intestinal bacterial overgrowth, common variable immunodeficiency, tropical sprue, Crohn disease, autoimmune enteropathy, and olmesartan-associated enteropathy if serology is negative but the biopsy is abnormal.
At Diagnosis, Look for the Consequences
- CBC and iron studies, ferritin, B12, folate, vitamin D, calcium -deficiencies are common and often the reason the patient presented.
- Liver enzymes (transaminitis is frequent and usually resolves on the diet), TSH given the autoimmune thyroid association.
- DEXA -celiac disease is a recognized cause of secondary osteoporosis, and this connects directly to the osteoporosis topic's secondary-cause workup.
- Screen first-degree relatives -a positive diagnosis is a family event, not just an individual one.
🚨 Management
The Gluten-Free Diet Is the Treatment
- Strict, lifelong elimination of wheat, barley and rye. Symptoms often improve within weeks; mucosal healing takes months to years in adults and is frequently incomplete, which is worth saying up front so patients do not interpret slow recovery as failure.
- Refer to a dietitian with celiac expertise -this is not optional advice. Hidden gluten in sauces, processed foods, medications and cross-contamination is the main reason diets fail, and label-reading is a taught skill.
- Oats are tolerated by most but must be certified gluten-free (cross-contamination during processing is the issue rather than oats themselves).
- Replace what is missing: iron, B12, folate, vitamin D and calcium as indicated; gluten-free products are often not fortified, so intake of B vitamins and fiber can fall on the diet.
- Immunizations: functional hyposplenism occurs in celiac disease, so ensure pneumococcal vaccination is current.
Follow-Up
- Recheck tTG-IgA at 6 and 12 months, then annually -falling titers indicate adherence, and a plateau or rise points to ongoing gluten exposure.
- Reassess symptoms, weight, nutritional labs and bone density; repeat DEXA per osteoporosis guidance where the initial scan was abnormal.
- Serology is a marker of adherence, not of healing -normal antibodies do not guarantee a healed mucosa, which is why persistent symptoms sometimes warrant repeat biopsy.
When the Patient Does Not Improve
- Continued gluten exposure is the answer in the large majority -usually inadvertent. Re-refer to the dietitian and review medications and supplements before considering anything exotic.
- Then consider coexisting conditions: lactose or fructose intolerance (common early, often transient), small intestinal bacterial overgrowth, microscopic colitis, pancreatic exocrine insufficiency, and functional overlap with IBS.
- Verify the original diagnosis -patients labeled celiac without confirmatory testing are common, and a wrong label produces a lifetime of unnecessary restriction.
- Refractory celiac disease is rare (persistent symptoms and villous atrophy despite 6-12 months of strict adherence) and belongs with a specialist center; it carries a risk of enteropathy-associated T-cell lymphoma, so new alarm features -weight loss, abdominal pain, fever, obstruction- in an established patient require prompt evaluation rather than dietary re-education.
Related Conditions Worth Distinguishing
- Non-celiac gluten sensitivity -symptoms with gluten but negative serology and normal biopsy on a gluten-containing diet. Real for the patient, but it is not celiac disease: no autoimmune enteropathy, no malignancy risk, no need to screen relatives, and the diet can be less absolute.
- Wheat allergy -IgE-mediated, with urticaria, angioedema or anaphylaxis, and a different testing pathway entirely.
- Dermatitis herpetiformis -treated with the gluten-free diet; dapsone controls the rash rapidly while the diet takes effect, and requires G6PD testing before starting.
🏥 Rounds
Pimp Questions
❓ A patient started a gluten-free diet 3 months ago and feels better. How do you diagnose celiac disease now?
You largely cannot, and that is the point of testing first. Serology normalizes and the mucosa heals within weeks to months off gluten, so both tTG-IgA and biopsy can be falsely negative. Two options remain: a formal gluten challenge -typically several weeks of adequate daily gluten before repeat serology and biopsy, which many patients decline because symptoms return- or HLA-DQ2/DQ8 typing, which is useful only to exclude: a negative result makes celiac disease essentially impossible, while a positive result occurs in a large share of the general population and proves nothing. The practical lesson is to test before advising dietary change.
❓ Why must total IgA be ordered alongside tTG-IgA?
Because selective IgA deficiency is substantially more common in celiac disease than in the general population, and an IgA-deficient patient cannot mount the antibody the test measures -producing a falsely negative tTG-IgA in exactly the population you are trying to diagnose. If total IgA is low, switch to IgG-based serology (deamidated gliadin peptide IgG or tTG-IgG). Ordering tTG-IgA alone is one of the commonest reasons celiac disease is missed on a first pass.
❓ A patient with confirmed celiac disease still has symptoms after a year on the diet. What is the most likely explanation?
Ongoing gluten exposure, usually inadvertent -hidden gluten in sauces, processed foods, medications and cross-contamination accounts for the large majority. Re-refer to a celiac-experienced dietitian before anything else. Then consider coexisting conditions: lactose or fructose intolerance, small intestinal bacterial overgrowth, microscopic colitis, pancreatic exocrine insufficiency, and IBS overlap. Verify the original diagnosis was properly confirmed. Refractory celiac disease is rare and belongs at a specialist center, and new alarm features raise concern for enteropathy-associated T-cell lymphoma.
❓ What is the commonest adult presentation of celiac disease?
Not classic diarrhea -the textbook malabsorptive picture is now a minority of adult cases, which is why the diagnosis is missed. The commonest presentations are extraintestinal: iron deficiency anemia unresponsive to oral iron (often the only clue), fatigue, osteoporosis or unexplained fracture, unexplained transaminitis, infertility or recurrent miscarriage, and neuropathy. GI symptoms, when present, are frequently bloating and pain that get labeled IBS for years. Practical rule: unexplained iron deficiency anemia deserves celiac serology.
❓ How many duodenal biopsies do you need, and why does the number matter?
At least four from the distal duodenum plus one or two from the duodenal bulb -because celiac disease is patchy, and sampling too few sites is a well-recognized cause of a falsely negative biopsy in a genuinely affected patient. Bulb biopsies matter because in some patients the changes are confined there. Remember also that villous atrophy is not specific to celiac disease: with negative serology and an abnormal biopsy, consider giardiasis, bacterial overgrowth, common variable immunodeficiency, tropical sprue, Crohn disease and olmesartan-associated enteropathy.
Sample Presentation
Ms. Novak is a 34-year-old woman referred for iron deficiency anemia unresponsive to 6 months of oral iron. Hemoglobin 10.4, ferritin 8, MCV 76. She reports bloating and intermittent loose stools attributed to IBS for several years, and has a sister with type 1 diabetes. She has not changed her diet. No overt bleeding; menses are normal.
Key Points: (1) Iron deficiency anemia refractory to oral iron, without a bleeding source, is a classic celiac presentation -the malabsorption is why the iron is not working. Send tTG-IgA with a total IgA now, while she is still eating gluten, and do not suggest a gluten-free trial before the results. (2) Her family history of autoimmune disease and the years of IBS labeling both fit the pattern of a diagnosis made late. (3) If serology is positive, proceed to duodenal biopsy with at least four distal samples plus bulb biopsies, then at diagnosis check B12, folate, vitamin D, calcium, liver enzymes and TSH, arrange DEXA, refer to a celiac-experienced dietitian, and screen her first-degree relatives.
Clinic Checklist
- Serology sent BEFORE any dietary change is suggested -the single most important sequencing rule.
- tTG-IgA ordered WITH total IgA; IgG-based testing substituted if IgA deficient.
- Adults biopsied to confirm, with at least four distal duodenal samples plus bulb biopsies.
- Nutritional consequences checked: iron, ferritin, B12, folate, vitamin D, calcium, liver enzymes, TSH.
- DEXA arranged -celiac disease is a secondary cause of osteoporosis.
- Dietitian referral made, not just diet advice given; pneumococcal vaccination confirmed.
- First-degree relatives advised to be screened.
- tTG-IgA rechecked at 6 and 12 months, then annually, as an adherence marker.
📋 Summary
Summary
Sequence Decides Everything
Test before the gluten-free diet starts. Serology normalizes and the mucosa heals within weeks to months off gluten, so a patient who has already stopped cannot be confirmed or excluded -leaving either a lifelong restrictive diet on no evidence or a missed diagnosis. If they have already stopped: gluten challenge, or HLA-DQ2/DQ8 typing which is useful only to EXCLUDE (negative rules it out; positive is common and proves nothing).
The Textbook Presentation Is the Minority
Most adults do not present with diarrhea and steatorrhea. The commonest clues are extraintestinal: iron deficiency anemia unresponsive to oral iron (often the only finding), fatigue, osteoporosis or unexplained fracture, transaminitis, infertility or recurrent miscarriage, and neuropathy. GI symptoms are frequently mislabeled IBS for years. Unexplained iron deficiency anemia earns celiac serology.
Order Total IgA With the tTG
tTG-IgA is first-line, but selective IgA deficiency is far more common in celiac disease than in the general population, and an IgA-deficient patient produces a falsely negative result. Low total IgA means switching to IgG-based testing (DGP-IgG or tTG-IgG). Ordering tTG-IgA alone is a leading reason the diagnosis is missed on the first pass; EMA-IgA confirms equivocal results.
Biopsy Adequately, and Read It Sceptically
Adults are confirmed by duodenal biopsy: at least four distal samples plus one or two from the bulb, because the disease is patchy and undersampling causes false negatives. Villous atrophy is not specific -with negative serology consider giardiasis, bacterial overgrowth, CVID, tropical sprue, Crohn disease and olmesartan-associated enteropathy.
Diagnosis Triggers a Workup, Not Just a Diet
Check iron, ferritin, B12, folate, vitamin D, calcium, liver enzymes and TSH; arrange DEXA, since celiac disease is a recognized secondary cause of osteoporosis. Confirm pneumococcal vaccination given functional hyposplenism. And screen first-degree relatives, whose risk is roughly ten-fold and who are often asymptomatic.
The Diet Needs a Dietitian
Strict lifelong avoidance of wheat, barley and rye, with a celiac-experienced dietitian as part of the treatment rather than an optional extra -hidden gluten and cross-contamination are the main causes of failure, and label-reading is a taught skill. Oats are fine if certified gluten-free. Warn that symptoms improve in weeks but mucosal healing takes months to years and is often incomplete in adults.
Follow the Titer, But Know Its Limits
Recheck tTG-IgA at 6 and 12 months then annually: falling titers indicate adherence, a plateau or rise indicates ongoing exposure. Serology tracks adherence, not healing -normal antibodies do not guarantee a healed mucosa, so persistent symptoms may still warrant repeat biopsy alongside nutritional and bone density reassessment.
Non-Response Is Usually Gluten
Continued, usually inadvertent, gluten exposure explains the large majority -re-refer to the dietitian before anything exotic, and verify the original diagnosis was actually confirmed. Then consider lactose or fructose intolerance, bacterial overgrowth, microscopic colitis, pancreatic insufficiency and IBS overlap. Refractory disease is rare, belongs at a specialist center, and carries lymphoma risk -new weight loss, pain or obstruction in an established patient needs prompt evaluation, not more dietary education.
