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The history of autoimmune disease, symptoms and associated microcytic anaemia are suggestive of Coeliac disease. The most commonly used screening test for Coeliac disease is checking for the presence of auto-antibodies against tissue transglutaminase (TTG). This has a high specificity and sensitivity; however, false negatives may be found in patients with IgA deficiency. IgA deficiency is more common in patient's with coeliac disease, and therefore, all patients should have IgA levels measured alongside antibodies against TTG. The next step in patients with IgA deficiency would be to measure antibodies against TTG from the IgG class
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Measure immunoglobulin G (IgG) TTG levels
QuestionChoice
Faecal calprotectin is a measure of intestinal inflammation. It may be raised in coeliac disease and conditions such as inflammatory bowel disease, colorectal cancer and infectious colitis. The main use of faecal calprotectin is to exclude inflammatory bowel disease (IBD), given that it has a high specificity in this context
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Measure faecal calprotectin
QuestionChoice
Low levels of faecal elastase are suggestive of exocrine pancreatic insufficiency. Causes include cystic fibrosis, chronic pancreatitis and biliary obstruction. Although the patient's symptoms may be due to pancreatic insufficiency, Coeliac disease is more likely given the history of autoimmune disease and IgA deficiency
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Measure faecal elastase
QuestionChoice
A duodenal biopsy is the gold standard test to confirm the diagnosis of Coeliac disease. It would be performed if serological tests are positive or if there is high clinical suspicion following multiple negative results from different serological tests
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Duodenal biopsy
QuestionChoice
This patient has IgA deficiency and likely has a false-negative IgA anti-TTG level. Repeating the anti-TTG levels using the same immunoglobulin class (i.e. IgA) is likely to give the same result
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Repeat anti-TTG antibody levels
QuestionComment
According to the answer "if there is enough clinical suspicion" to do a duodenal biopsy- does the history and blood results not give us a high enough level of clinical suspicion? 
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# Summary

Coeliac disease is a T cell-mediated autoimmune condition characterised by the body's inflammatory response to dietary gluten, leading to small bowel damage and malabsorption. Key signs and symptoms include gastrointestinal disturbances such as diarrhoea, abdominal pain, nausea, vomiting, and systemic symptoms like fatigue, weight loss or failure to thrive in children. Additionally, dermatitis herpetiformis may be observed. The gold standard for diagnosis involves an oesophago-gastroduodenoscopy (OGD) and duodenal/jejunal biopsy, supplemented by serological tests like anti-TTG IgA antibody measurement. The primary management strategy is a lifelong adherence to a gluten-free diet, alongside regular monitoring for complications. 

# Definition

Coeliac disease is a T cell-mediated autoimmune disorder affecting the small intestine. The condition arises due to the production of an auto-antibody against gluten, specifically its component called prolamin, which results in inflammation and villous atrophy of the small bowel leading to malabsorption.

# Epidemiology

Coeliac disease is a prevalent chronic disorder, affecting roughly 0.5 to 1 percent of the general population worldwide. In areas such as Europe, the United States, and Australia, the prevalence varies, ranging from 1 in 80 to 1 in 300 children. The condition disproportionately affects females, with a female to male ratio of approximately 2:1. Coeliac disease exhibits a bimodal age of onset, presenting either in infancy or between the ages of 50-60. It is notably more prevalent in individuals of Irish descent.

# Aetiology

Coeliac disease is associated with a positive family history, the presence of the HLA-DQ2 allele, and other autoimmune diseases, including type 1 diabetes mellitus.

# Signs and Symptoms

Gastrointestinal symptoms include:

- Abdominal pain
- Distension
- Nausea and vomiting
- Diarrhoea
- **Steatorrhoea** (indication of severe disease)

Systemic symptoms encompass:

- Fatigue
- **Weight loss or failure to thrive in children** (indication of severe disease)

Physical examination may reveal:

- Pallor (secondary to anaemia)
- **Short stature and wasted buttocks** (secondary to malnutrition)
- Signs of vitamin deficiency due to malabsorption (e.g., bruising secondary to vitamin K deficiency)
- Dermatological manifestations: **dermatitis herpetiformis** (pruritic papulovesicular lesions over the buttocks and extensor surfaces of the arms, legs, and trunk).
- Abdominal distension

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# Differential Diagnosis

The main differential diagnoses for coeliac disease include:

- **Irritable bowel syndrome (IBS)**: Characterised by chronic abdominal pain, bloating, and altered bowel habits without any organic cause.
- **Inflammatory bowel disease (IBD)**: Crohn's disease and ulcerative colitis are forms of IBD and may present with abdominal pain, diarrhoea, weight loss, and systemic signs of inflammation.
- **Food intolerance/allergy**: Abdominal discomfort, bloating, and diarrhoea are common.
- **Gastroenteritis**: Acute diarrhoea and vomiting, often with fever.
- **Malabsorption syndromes (other than coeliac disease)**: Chronic diarrhoea, weight loss, and signs of specific nutrient deficiencies.

# Investigations

Bedside:

- Stool culture to exclude infectious causes. A faecal calprotectin may also be done as IBD is a differential.

Bloods:

- Blood tests include FBC, U&E, bone profile, LFT, Iron, B12, and Folate levels.
	- It is important to screen for conditions related to malabsorption such as mixed anaemias, vitamin deficiencies.
- First line serological tests such as anti-TTG IgA antibody and IgA level, followed by anti-TTG IgG, anti-endomyseal antibody, (anti-gliadin is not recommended by NICE.)

Imaging/Invasive:

- Oesophago-gastroduodenoscopy (OGD) and duodenal/jejunal biopsy, is considered the gold standard for diagnosis.
- Histology typically reveals sub-total villous atrophy, crypt hyperplasia, and intra-epithelial lymphocytes.

NB: in the context of antibody blood tests and OGDs looking for changes, the patient needs to have been eating gluten for 6 weeks prior to the investigation.

# Management

- Primary management of coeliac disease is a lifelong commitment to a gluten-free diet. Patient education about food items containing gluten is crucial.
- Common food items which contain gluten include bread, pasta, pastries and most beers.
- Regular monitoring of the patient is necessary to ensure adherence to the diet and screen for potential complications. Serological tests can also be done to assess response to removing dietary gluten intake.
- Dermatitis herpetiformis is managed with dapsone

# Complications

- Mixed anaemia
- Hyposplenism (increasing susceptibility to encapsulated organisms). Patients with coeliac disease therefore require annual flu and one-off pneumovax vaccinations
- Osteoporosis (a DEXA scan may be needed)
- Enteropathy-associated T cell lymphoma (EATL; a rare type of non-Hodgkin lymphoma), the likelihood of which is proportional to the strength of adherence to a gluten-free diet.

# NICE Guidelines

[Click here to see information on NICE CKS about coeliac disease](https://cks.nice.org.uk/topics/coeliac-disease/)
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In patients with suspected Coeliac disease and low serum IgA, measure IgG anti-tissue transglutaminase (TTG) antibodies for accurate diagnosis.
A 32-year-old with type 1 diabetes presents to her GP with a 6-month history of diarrhoea, weight loss and bloating.

Examination reveals conjunctival pallor and a soft, non-tender abdomen.

Her blood tests show a microcytic anaemia, thrombocytopenia, normal anti-tissue transglutaminase (TTG) antibody levels and low serum immunoglobulin A (IgA).

Which of the following is the next best investigation given the likely diagnosis?
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