Case Study  


Celiac disease versus IBS: is it really such a clinical conundrum? 

July 2018   

Gemma, a 30-year-old woman from Windsor, had been suffering with ill health for over a decade by the time she attended an appointment with her GP in July 2018.


Between the ages of 14 and 17, Gemma presented several times to primary care, due to abdominal cramping and stomach upset in connection with food intake. During that period of time, the GP advised her to ensure she followed a healthy, varied and fiber-rich diet.



At the age of 19, Gemma presented to her GP again, with feeding difficulties, abdominal pain, mild diarrhea, and general malaise/fatigue. Her full blood count and hematinics were normal. She was then referred for a colonoscopy, which did not show any abnormalities. The GP told Gemma that the most likely cause of her symptoms was irritable bowel syndrome (IBS), and no further investigations were performed.


Gastrointestinal symptoms alone cannot accurately differentiate celiac disease from IBS;1 organic diseases such as celiac disease should be ruled out before a diagnosis of IBS is made.2

Celiac disease has a prevalence of 1 percent in the general population,3 and up to 4.7 percent in patients who were diagnosed with IBS based on symptom criteria.





Between the ages of 23 and 29, Gemma experienced three complicated pregnancies. With all three, she suffered from intense pruritis during the last two trimesters, with very high levels of serum bilirubin and alanine aminotransferase. Intrahepatic cholestasis of pregnancy was determined to be the cause, and the pruritis spontaneously resolved in the postnatal period. All three children were born prematurely.


Celiac disease is associated with high miscarriage rates, intrauterine growth retardation, low birth weight, and preterm birth.




July 2018  

By the time of her GP appointment in July 2018, Gemma had been struggling with her bowel symptoms for the past 11 years. 


Gemma, aged 30 years: “The pain and disease fill so much of my everyday life.

Over the years, Gemma’s symptoms had evolved; she now had a very poor appetite, weight loss, and rashes and blister-like lesions on her elbows.

Gemma’s GP ordered thyroid function tests and checked her vitamin D levels.

  • Thyroid stimulating hormone (TSH): high (5.2 mU/L)
  • Free thyroxine (FT4): lower limit of normal (12 pmol/L)
  • Vitamin D: low (18 nmol/L)

The GP postulated that Gemma’s vitamin D deficiency could be the reason for many of her symptoms and prescribed once-daily cholecalciferol capsules (1,400 IU). 




January 2019: 6-month follow-up appointment 

6 months later, Gemma’s TSH was still mildly elevated, her FT4 was still on the lower limit of normal, and her vitamin D levels had returned to normal. Given that she no longer had vitamin D deficiency, which was thought to be the cause of her illness, she felt pressured to ‘feel better’. However, her symptoms had not improved.



  • Slept 9-10 hours every day
  • Had dry, blistery skin on her elbows
  • Suffered with depression and stress

Despite all this, she had become so used to her poor toilet habits that she no longer noticed them; they had become part of her everyday life.

Around this time, Gemma began to keep a diary, and realized that her symptoms seemed to be linked to food consumption, but with no clear pattern of what food they might have been related to. 




July 2019: 6 months later, Gemma presented to primary care again

At the age of 31, Gemma’s bowel habits had significantly worsened, triggering a return to her GP. She showed the GP the diary which she had been keeping, after which the GP decided to test for celiac disease and food allergy. As she also had a history of mildly elevated TSH, the GP added in a test for autoimmune thyroid disease.


Gemma’s blood results were as follows:

  • Tissue transglutaminase (tTG) IgA: positive (118 U/mL, 12x ULN)
  • Total IgA: normal (2.1 g/L)
  • Specific IgE to a panel of food allergens, including wheat: negative (<0.1 kAU/L)
  • Anti-thyroid peroxidase (TPO) antibodies: positive (2,400 IU/mL) 

tTG IgA is the recommended first-line test for celiac disease, together with total IgA to check for IgA deficiency.




New diagnosis

Based on the results of her most recent blood tests and following confirmation by a gastroenterologist, Gemma’s primary diagnosis was changed from IBS to celiac disease. Gemma was advised to begin a strict gluten-free diet and to carry on keeping her diary—taking particular care to log food and symptoms. 


Gemma, aged 31 years: “Finally there is a blood test that can answer some of the many symptoms I have had for many years.

Given Gemma’s sharply elevated anti-TPO antibodies, the GP referred her to an endocrinologist. 

It takes, on average, 13 years to receive a correct diagnosis of celiac disease.




September 2019


Gemma’s endocrinologist ran further thyroid-function and antibody tests and found that she had subclinical Hashimoto’s thyroiditis. This did not require treatment but was to be reviewed on a 3-monthly basis. 

Serological signs of autoimmune thyroid disease have been found in up to 26 percent of patients with celiac disease.




July 2020

By mid-2020, Gemma had completed 1 year of a strict gluten-free diet. Her bowel habits were much improved, but she still suffered with muscle pain, dry skin, malaise/fatigue, and depression. 


Her tTG IgA levels were falling (43 U/mL, 4x ULN), but TSH was still elevated and FT4 had dropped below the lower limit of normal. She was subsequently diagnosed with hypothyroidism secondary to Hashimoto’s thyroiditis, and began treatment with levothyroxine.

It is common practice for tTG IgA to be tested every 3 months, until normalized, and once a year as an indicator of diet adherence.




September 2020: Following 2 months of treatment


Following 2 months of treatment with levothyroxine, Gemma’s: 
  • TSH was improving and FT4 normalized
  • Muscle pain was almost gone
  • Fatigue and depression were resolved    

Gemma, aged 32 years: “I am relieved to finally feel I have received answers to the inconveniences and the malaise. But, at the same time, I feel despair and frustration, and have a lot of unanswered questions. Have I had it for a long time? So, I have REALLY been sick—despite previously coming to the conclusion that it had to be something mental and not physical.




Would you ever make a diagnosis of IBS without first using a tTG IgA blood test to screen for celiac disease?

Yes No

This is a fictional case study, and the image used is of a model.
FT4: free thyroxine; IgA: immunoglobulin A; IgE: immunoglobulin E; TSH: thyroid-stimulating hormone; tTG: tissue transglutaminase; ULN: upper limit of normal

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