Introduction We have previously shown that thyroid peroxidase antibodies (TPO) are more commonly found in patients with coeliac disease (CD) compared to controls and raised titres are associated with an increased risk of thyroid disease. Some studies have suggested that compliance reduces the risk of other autoimmune disease including thyroid dysfunction. The relationship between dietary adherence and TPO titre is not known. We sought to assess the changes in TPO before and after a gluten free diet (GFD). Furthermore, we also investigated whether HLA type has any influence on the prevalence of thyroid disease and TPO in these patients.

Methods Patients were recruited from the specialist coeliac clinic. Demographic details, current thyroid status (including TPO level), HLA status, duration of both CD and thyroid disease were recorded. Tissue-transglutaminase antibodies (tTG) were measured at baseline along with TPO. At follow-up both antibody titres were measured and compared to baseline values.

Results 36/120 patients were excluded from analysis due to incomplete tTG and TPO testing. 84 patients with CD had sequential TTG and TPO analysis (mean age 48, 25 males, and median duration of follow-up 3 years). At baseline 19/84 (22.6%) had positive TPO (normal <50 iu/ml) compared to 18/84 (21.4%) at follow-up. On analysis of tTG with unpaired t test, individuals with positive TPO had a trend towards higher tTG antibodies at baseline (229 vs 174, p=0.08) and a significantly higher tTG at follow-up (96 vs 44, p=0.03). We did not find any significant difference between TPO titres at diagnosis and follow-up (Mean TPO titre; at diagnosis=340, at follow-up=274, p=0.68). HLA status was tested on 88/120 patients (21/88 HLA DQ2 homozygotes, 61/88 HLA DQ2 heterozygotes and 6/88 were HLA DQ 8) Patients who were heterozygous for HLA DQ2 were significantly more likely than patients who were homozygous for HLA DQ8 to have raised TPO titres (21/61 heterozygotes were TPO positive compared to 2/21 homozygotes, OR 5.0, CI 1.1 to 23.5, p=0.046.

Conclusion TPO positivity is common in patients with coeliac disease. This study uniquely shows that TPO positivity is predictive of higher tTG at follow-up. In addition we have also shown that CD patients with HLA DQ2 homozygosity have a reduced TPO titre.