25 August 2017

Time to get more active in looking for coeliac disease

Clinical Nutrition

Actively looking for coeliac disease in high-risk patients, or those with unexplained symptoms, may help prevent under-diagnosis of coeliac disease, a paper in the MJA has argued.

There could be as many as 80% of people with coeliac disease in Australia who had not been diagnosed, Marjorie Walker, the lead author and a professor of anatomical pathology at the University of Newcastle, said.

Some patients with undiagnosed coeliac disease took it upon themselves to cut gluten out of their diet without GP input.

Others continued to consume gluten, putting them at risk of nutritional deficiencies, reduced bone mineral density, refractory coeliac disease and cancer.

Coeliac disease affects up to 2% of Australians.

“Coeliac disease is quite common, but we are missing it,” Professor Walker said.

“It would be good if GPs could think about coeliac disease when a patient doesn’t have classical symptoms, such as diarrhoea,” she said.

Coeliac disease could be considered when a patient presented with severe or persistent mouth ulcers, type 1 diabetes, autoimmune thyroid disease or when the patient had a first-degree relative with coeliac disease, Professor Walker said.

The MJA paper also listed prolonged fatigue; irritable bowel syndrome; unexpected weight loss; faltering growth; persistent, unexplained abdominal or gastrointestinal symptoms; and unexplained iron, vitamin B12 or folate deficiency as potential signs of undiagnosed coeliac disease.

The best way to diagnose coeliac disease was to start with serology and follow up with a biopsy of the duodenum to confirm, Professor Walker said.

A total IgA and IgA tissue transglutaminase (tTG) was the first choice for serology testing.

“If the IgA tTG test is weakly positive, consider using the IgG deamidated gliadin peptide test to confirm the diagnosis, or if the IgA level is deficient, then use the IgG tTG test,” the MJA paper said.

Both the blood test and biopsy required the patient to be on a gluten-containing diet to avoid a false-negative result.

If the patient was already on a gluten-free diet at presentation, the GP could give them a gluten challenge, defined as 8 to 10g of gluten (about four slices of wheat bread) per day for six to eight weeks.

If the patient refused to consume gluten, GPs could conduct genotyping, which had some predictive value.

Human leucocyte antigen class II haplotypes DQ2 and DQ8 are found in nearly all patients with coeliac disease. Patients who lack both genes are very unlikely to have coeliac disease (with 99% accuracy).

However, the rate of false positives was high, because as many as 56% of Australians have at least one of these genes.

“This is not a frontline test at all,”  Professor Walker said.

Around 20% of Australians were already following a gluten-free diet. But it was also important to diagnose or rule out coeliac disease in this group, because giving up gluten was socially restrictive, particularly for children, and had unknown health impacts, Professor Walker said.

MJA 2017, 21 August