Celiac Disease in Adults: Symptoms, What Else It Could Be, and How to Get Tested

Why is celiac disease often diagnosed late?

Celiac disease presents so differently from person to person that it is easily labeled as IBS, anxiety, or a "sensitive stomach" for years before anyone thinks to test for it 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk. The condition affects roughly 1 in 100 people worldwide and is frequently undiagnosed — and not everyone with celiac has obvious GI symptoms 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

Many adults present primarily with fatigue, 3Ref 3National Institute of Diabetes and Digestive and Kidney Diseases (2020).Celiac Disease.Overview of celiac disease prevalence (~1 in 100 worldwide), dermatitis herpetiformis as an extra-intestinal manifestation, and the importance of testing before dietary changes iron-deficiency anemia that does not respond to iron supplements, bone density loss (osteoporosis), infertility, mouth sores (aphthous ulcers), a specific blistering skin rash called dermatitis herpetiformis, or neurological symptoms. The GI symptoms that do occur — diarrhea, bloating, cramping, gas — overlap significantly with IBS and other common conditions.

What are the symptoms of celiac disease in adults?

GI symptoms include chronic diarrhea (often pale, fatty, or foul-smelling because fat is not being absorbed properly), bloating, gas, abdominal cramping, nausea, and constipation in some adults. These may come and go.

Non-GI symptoms that can be the primary or only presentation include 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk: - Persistent fatigue that does not improve with rest - Iron-deficiency anemia (often the first clue in adults) - Folate or vitamin B12 deficiency - Bone or joint pain; osteoporosis or stress fractures in younger adults - Mouth sores (aphthous ulcers) - A blistering, itchy rash on elbows, knees, or buttocks (dermatitis herpetiformis) - Brain fog or difficulty concentrating - Anxiety or depression - Tingling or numbness in hands or feet - Irregular menstrual periods, recurrent miscarriage, or difficulty conceiving

It is common to have only a few of these, or to have them mildly for years before the pattern becomes clear. This is why the average time from first symptoms to diagnosis is measured in years, not weeks 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

What else could cause these symptoms? Celiac vs. IBS vs. gluten sensitivity

Non-celiac gluten sensitivity (NCGS) is a real condition involving symptoms triggered by gluten, but without the immune damage or intestinal damage of celiac disease. There is no blood test or biopsy that confirms NCGS — it is a diagnosis of exclusion after celiac and wheat allergy have been ruled out 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

The practical difference matters: celiac disease causes lasting intestinal damage and nutrient malabsorption even from small amounts of gluten (strict lifelong avoidance is necessary), while NCGS may be managed with less strict reduction.

IBS is frequently confused with celiac — recurring cramping and bowel changes linked to stress and multiple food types, not specifically gluten. No anemia, weight loss, or nutritional deficiencies are present. IBS and celiac can also co-exist 2Ref 2Lacy BE, Pimentel M, Brenner DM, Chey WD, Keefer LA, Long MD, Moshiree B (2021).ACG Clinical Guideline: Management of Irritable Bowel Syndrome.IBS as a condition frequently confused with or co-occurring with celiac disease; ruling out celiac before diagnosing IBS.

Wheat allergy involves rapid-onset symptoms (hives, swelling, difficulty breathing, or GI upset) within minutes to hours of eating wheat — a different immune mechanism from celiac.

Inflammatory bowel disease (Crohn's or ulcerative colitis) is worth ruling out when diarrhea and GI symptoms are prominent — particularly if there is blood in the stool, fever, or significant weight loss.

The most important rule: do not go gluten-free before testing

This is the most practically important point in this article. The blood tests for celiac — especially the anti-tissue transglutaminase IgA antibody (tTG-IgA) — look for immune reactions triggered by gluten. If you have already significantly reduced or eliminated gluten before testing, those antibodies will fall, and the test will return negative even if you have celiac disease. The same is true for the small intestinal biopsy 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

If you suspect celiac: book a clinician appointment and keep eating your normal diet in the meantime. If you have already gone gluten-free and want to test, you will need to eat a meaningful amount of gluten for several weeks beforehand — a "gluten challenge." A clinician should supervise this, as it can temporarily worsen symptoms.

Getting the right diagnosis matters for how strictly and permanently you need to avoid gluten.

What does testing for celiac disease involve?

Initial blood tests: The primary screen is the tTG-IgA antibody, always paired with a total IgA level — because IgA deficiency (which is relatively common) can cause a false-negative result. An endomysial antibody (EMA-IgA) may also be ordered as a highly specific confirmatory test 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

Small intestinal biopsy: If blood tests are positive or strongly suggestive, the next step is usually a biopsy taken during an upper endoscopy. The biopsy looks for villous atrophy — flattening of the small intestinal lining that impairs nutrient absorption. This is the diagnostic gold standard.

Nutritional assessment: Blood tests for iron, B12, folate, vitamin D, and calcium are important both to help confirm the impact of celiac and to identify deficiencies that need treatment.

HLA-DQ2/DQ8 genetic testing: Not diagnostic on its own, but a negative result makes celiac very unlikely — useful in special situations such as when someone is already gluten-free and a gluten challenge is not feasible.

If both blood tests and biopsy are negative and you have been eating gluten normally, celiac is effectively ruled out 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.

Who is at higher risk and should be tested more readily?

• First-degree relatives of someone with celiac disease (risk is meaningfully elevated)
• People with other autoimmune conditions such as type 1 diabetes or thyroid disease
• People with unexplained iron-deficiency anemia or osteoporosis at a young age
• Women with unexplained recurrent miscarriage or infertility
• Anyone already eating gluten-free who wants a proper diagnosis

Family members of a confirmed celiac patient should also be considered for testing, even without prominent symptoms 1Ref 1Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Greer KB, Limketkai BN, Lebwohl B (2023).American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.Full celiac disease presentation, diagnostic criteria (tTG-IgA, EMA, biopsy), importance of gluten consumption before testing, gluten challenge, HLA testing, NCGS distinction, family risk.