Coeliac disease: who to test, serology, follow-up on a gluten-free diet

Laboratory tests (on a gluten-containing diet)

• IgA anti-tissue transglutaminase antibodies (tTG-IgA)
• Total IgA (serum level)
• IgG anti-tissue transglutaminase antibodies (if IgA deficiency: total IgA < 0.07 g/L)if neededIgA deficiency (2 to 3% of patients): IgG-class tests ^[1], reimbursed in this situation ^[2]. Deficiency defined by total IgA < 0.07 g/L; IgG anti-transglutaminase is then the first-line test ^[3].
• IgA anti-endomysial antibodies, on a second sample (child whose IgA anti-transglutaminase is ≥ 10 times normal, without type 1 diabetes)if neededIn children, IgA anti-transglutaminase ≥ 10 times the upper limit of normal: IgA anti-endomysial antibodies on a second sample before the paediatric gastroenterologist's opinion; if positive, they allow diagnosis without biopsy ^[3,4]. In adults, no test other than anti-transglutaminase is recommended: refer to the gastroenterologist as soon as they are positive ^[3].
• HLA class II typing, DQ2/DQ8 (only if gluten reintroduction is refused or poorly tolerated)if neededAlternative to gluten reintroduction: absence of a susceptibility haplotype rules out the disease; its presence (about 40% of the population) proves nothing and requires reintroduction before testing ^[3]. Can be prescribed by any doctor, with the signed attestation of consultation and consent (document supplied by the laboratory) ^[3].
• On a gluten-containing diet. If gluten has been reduced or removed: reintroduce it for 6 to 8 weeks (at least 3 g a day, preferably 8 to 10 g; 3 g = 2 slices of sandwich bread or 1/6 of a baguette) before the assay. Do not start the gluten-free diet before the diagnosis is confirmed.

Laboratory tests

• FBC
• Serum ferritin
• Folate (vitamin B9)
• Vitamin B12
• Serum calcium
• Alkaline phosphatase
• 25-hydroxyvitamin D
• Bone densitometry if high risk of osteoporosis (not a laboratory test).
• First-degree relatives: serology (IgA anti-transglutaminase and total IgA), from age 3, repeated every 5 years or if symptoms appear.

At 6 months then at 12 months of diet

• IgA anti-tissue transglutaminase antibodies (IgG if IgA deficiency)
• Follow-up of abnormalities in the initial tests (FBC, ferritin, folate, B12…)if needednon-French guidelineCheck that the abnormalities present at diagnosis have normalised ^[1].

Then once a year (annual review)

• IgA anti-tissue transglutaminase antibodies (tTG-IgA)if needednon-French guidelineAdherence monitoring combines history and serology ^[1].
• TSHif needednon-French guidelineAnnual review by the BSG (UK, 2014), once the disease is stable: TSH and thyroid hormones for an associated autoimmune disease, AST and ALT for liver involvement, in addition to the absorption tests and serology ^[9]; the ACG (2023) also cites transaminases among the possible monitoring tests ^[7]. In France, HAS has published only the diagnostic part, the part on management and follow-up being announced ^[3].
• ASTif needednon-French guidelineAnnual review by the BSG (UK, 2014), once the disease is stable: TSH and thyroid hormones for an associated autoimmune disease, AST and ALT for liver involvement, in addition to the absorption tests and serology ^[9]; the ACG (2023) also cites transaminases among the possible monitoring tests ^[7]. In France, HAS has published only the diagnostic part, the part on management and follow-up being announced ^[3].
• ALTif needednon-French guidelineAnnual review by the BSG (UK, 2014), once the disease is stable: TSH and thyroid hormones for an associated autoimmune disease, AST and ALT for liver involvement, in addition to the absorption tests and serology ^[9]; the ACG (2023) also cites transaminases among the possible monitoring tests ^[7]. In France, HAS has published only the diagnostic part, the part on management and follow-up being announced ^[3].