How much, for how long?
Gluten free diets are gaining in popularity for relief of gastrointestinal symptoms and are often undertaken before people have been adequately screened for coeliac disease. Once improved, many are then unwilling or unable to undergo a prolonged gluten challenge for fear of developing a severe recurrence of symptoms. A standard gluten challenge consists of the equivalent of 2 serves of gluten containing food (~10 g) per day for up to 8 weeks, followed by serological testing and small bowel biopsy. This amount and duration of gluten ingestion is often poorly tolerated, and there has been considerable interest in developing abbreviated challenge protocols to improve adherence without sacrificing diagnostic sensitivity. A recent study by Leffler et al has shown that:
- Over 75% of adults will meet diagnostic criteria for coeliac disease after a 2-week gluten challenge.
- No differences were seen between 3 and 7.5 g of gluten per day suggesting that high doses of gluten exposure are not routinely needed.
- Antibody response in coeliac disease is delayed in comparison with measurable histological changes.
- Coeliac serological titres continue to rise significantly after the end of gluten challenge.
Based on these results, if a patient is already on a gluten free diet at presentation, it is reasonable to recommend the following diagnostic approach:
- perform baseline serology (IgA anti-tTG and IgG anti-gliadin) and HLA DQ2/8 genotyping;
- proceed to small bowel biopsy if serological results are >2x upper limit of normal;
- if not, undertake challenge with 3 g gluten per day (equivalent to ~1½ slices of bread) for 2-3 weeks (or longer if tolerated);
- wait a further 2 weeks after the end of the challenge, then repeat serology and perform small bowel biopsy.
Some authorities consider that small bowel biopsy is unnecessary in children and adolescents if they are HLA DQ2/8 positive and their anti-tTG levels are very high. However, I still advise all parents to get their children biopsied unless they have compelling reasons not to do so, for the following reasons:
- No single test is 100% reliable.
- Coeliac disease is a diagnosis they will carry for the rest of their lives.
- The diagnosis has important implications for current & future family members.
- There is value in assessing severity of mucosal disease on small bowel biopsy at the outset and to have a baseline for comparison if there are future glitches.
Leffler D, Schuppan D, Pallav K et al. Kinetics of the histological, serological and symptomatic responses to gluten challenge in adults with coeliac disease. Gut Online First, May 22, 2012 doi:10.1136/gutjnl-2012-302196