Diagnosis is often difficult and as of 2019, there continues to be a lack of awareness among physicians about the variability of presentations of<unk>  and the diagnostic criteria, such that most cases are diagnosed with great delay. It can take up to 12 years to receive a diagnosis from the onset of symptoms and the majority of those affected in most countries never receive it. Several tests can be used. The level of symptoms may determine the order of the tests, but all tests lose their usefulness if the person is already eating a gluten-free diet. Intestinal damage begins to heal within weeks of gluten being removed from the diet, and antibody levels decline over months. For those who have already started on a gluten-free diet, it may be necessary to perform a rechallenge with some gluten-containing food in one meal a day over 6 weeks before repeating the investigations. Blood tests Immunofluorescence staining pattern of endomysial antibodies on a monkey oesophagus tissue sample. Serological blood tests are the first-line investigation required to make a diagnosis of<unk> . Its sensitivity correlates with the degree of histological lesions. People who present with minor damage to the small intestine may have seronegative findings so many patients with<unk>  often are missed. In patients with villous atrophy, anti-endomysial (EMA) antibodies of the immunoglobulin A (IgA) type can detect<unk>  with a sensitivity and specificity of 90% and 99%, respectively. Serology for anti-transglutaminase antibodies (anti-tTG) was initially reported to have a higher sensitivity (99%) and specificity (>90%). However, it is now thought to have similar characteristics to anti-endomysial antibodies. Both anti-transglutaminase and anti-endomysial antibodies have high sensitivity to diagnose people with classic symptoms and complete villous atrophy, but they are only found in 30–89% of the cases with partial villous atrophy and in less than 50% of the people who have minor mucosal lesions (duodenal lymphocytosis) with normal villi. Tissue transglutaminase modifies gluten peptides into a form that may stimulate the immune system more effectively. These peptides are modified by tTG in two ways, deamidation or transamidation. Modern anti-tTG assays rely on a human recombinant protein as an antigen. tTG testing should be done first as it is an easier test to perform. An equivocal result on tTG testing should be followed by anti-endomysial antibodies. Guidelines recommend that a total serum IgA level is checked in parallel, as people with<unk>  with IgA deficiency may be unable to produce the antibodies on which these tests depend ("false negative"). In those people, IgG antibodies against transglutaminase (IgG-tTG) may be diagnostic. If all these antibodies are negative, then anti-DGP antibodies (antibodies against deamidated gliadin peptides) should be determined. IgG class anti-DGP antibodies may be useful in people with IgA deficiency. In children younger than two years, anti-DGP antibodies perform better than anti-endomysial and anti-transglutaminase antibodies tests. Because of the major implications of a diagnosis of<unk> , professional guidelines recommend that a positive blood test is still followed by an endoscopy/gastroscopy and biopsy. A negative serology test may still be followed by a recommendation for endoscopy and duodenal biopsy if clinical suspicion remains high. Historically three other antibodies were measured: anti-reticulin (ARA), anti-gliadin (AGA) and anti-endomysial (EMA) antibodies. ARA testing, however, is not accurate enough for routine diagnostic use. Serology may be unreliable in young children, with anti-gliadin performing somewhat better than other tests in children under five. Serology tests are based on indirect immunofluorescence (reticulin, gliadin and endomysium) or ELISA (gliadin or tissue transglutaminase, tTG). Other antibodies such as anti–Saccharomyces cerevisiae antibodies occur in some people with<unk>  but also occur in other autoimmune disorders and about 5% of those who donate blood. Antibody testing may be combined with HLA testing if the diagnosis is unclear. TGA and EMA testing are the most sensitive serum antibody tests, but as a negative HLA-DQ type excludes the diagnosis of<unk> , testing also for HLA-DQ2 or DQ8 maximises sensitivity and negative predictive values. In the United Kingdom, the National Institute for Health and Clinical Excellence (NICE) does not (as of 2015) recommend the use of HLA typing to rule out<unk>  outside of a specialist setting, for example, in children who are not having a biopsy, or in patients who already have limited gluten ingestion and opt not to have a gluten challenge. Endoscopy Endoscopic still of duodenum of a person with<unk>  showing scalloping of folds and "cracked-mud" appearance to mucosa jejunal pathology in<unk> . An upper endoscopy with biopsy of the duodenum (beyond the duodenal bulb) or jejunum is performed to obtain multiple samples (four to eight) from the duodenum. Not all areas may be equally affected; if biopsies are taken from healthy bowel tissue, the result would be a false negative. Even in the same bioptic fragment, different degrees of damage may be present. Most people with<unk>  have a small intestine that appears to be normal on endoscopy before the biopsies are examined. However, five findings have been associated with high specificity for<unk> : scalloping of the small bowel folds (pictured), paucity in the folds, a mosaic pattern to the mucosa (described as a "cracked-mud" appearance), prominence of the submucosa blood vessels, and a nodular pattern to the mucosa. European guidelines suggest that in children and adolescents with symptoms compatible with<unk> , the diagnosis can be made without the need for intestinal biopsy if anti-tTG antibodies titres are very high (10 times the upper limit of normal). Until the 1970s, biopsies were obtained using metal capsules attached to a suction device. The capsule was swallowed and allowed to pass into the small intestine. After x-ray verification of its position, suction was applied to collect part of the intestinal wall inside the capsule. Often-utilised capsule systems were the Watson capsule and the Crosby–Kugler capsule. This method has now been largely replaced by fibre-optic endoscopy, which carries a higher sensitivity and a lower frequency of errors. Capsule endoscopy (CE) allows identification of typical mucosal changes observed in<unk>  but has a lower sensitivity compared to regular endoscopy and histology. CE is therefore not the primary diagnostic tool for<unk> . However, CE can be used for diagnosing T-cell lymphoma, ulcerative jejunoileitis, and adenocarcinoma in refractory or complicated<unk> . Pathology The classic pathology changes of<unk>  in the small bowel are categorised by the "Marsh classification": * Marsh stage 0: normal mucosa * Marsh stage 1: increased number of intra-epithelial lymphocytes (IELs), usually exceeding 20 per 100 enterocytes * Marsh stage 2: a proliferation of the crypts of Lieberkühn * Marsh stage 3: partial or complete villous atrophy and crypt hypertrophy * Marsh stage 4: hypoplasia of the small intestine architecture Marsh's classification, introduced in 1992, was subsequently modified in 1999 to six stages, where the previous stage 3 was split in three substages. Further studies demonstrated that this system was not always reliable and that the changes observed in<unk>  could be described in one of three stages: * A representing lymphocytic infiltration with normal villous appearance; * B1 describing partial villous atrophy; and * B2 describing complete villous atrophy. The changes classically improve or reverse after gluten is removed from the diet. However, most guidelines do not recommend a repeat biopsy unless there is no improvement in the symptoms on diet. In some cases, a deliberate gluten challenge, followed by a biopsy, may be conducted to confirm or refute the diagnosis. A normal biopsy and normal serology after challenge indicates the diagnosis may have been incorrect. In untreated<unk> , villous atrophy is more common in children younger than three years, but in older children and adults, it is common to find minor intestinal lesions (duodenal lymphocytosis) with normal intestinal villi. Other diagnostic tests At the time of diagnosis, further investigations may be performed to identify complications, such as iron deficiency (by full blood count and iron studies), folic acid and vitamin B12 deficiency and hypocalcaemia (low calcium levels, often due to decreased vitamin D levels). Thyroid function tests may be requested during blood tests to identify hypothyroidism, which is more common in people with<unk> . Osteopenia and osteoporosis, mildly and severely reduced bone mineral density, are often present in people with<unk> , and investigations to measure bone density may be performed at diagnosis, such as dual-energy X-ray absorptiometry (DXA) scanning, to identify the risk of fracture and need for bone protection medication. Gluten withdrawal Although blood antibody tests, biopsies, and genetic tests usually provide a clear diagnosis, occasionally the response to gluten withdrawal on a gluten-free diet is needed to support the diagnosis. Currently, gluten challenge is no longer required to confirm the diagnosis in patients with intestinal lesions compatible with<unk>  and a positive response to a gluten-free diet. Nevertheless, in some cases, a gluten challenge with a subsequent biopsy may be useful to support the diagnosis, for example in people with a high suspicion for<unk> , without a biopsy confirmation, who
Coeliac disease
Inflammatory bowel disease
Tropical sprue
Cystic fibrosis
Hereditary diffuse gastric cancer
Intestinal parasite infection
Crohn's disease
Irritable bowel syndrome