The safe threshold for gluten contamination in gluten-free products. Can trace amounts be accepted in the treatment of coeliac disease?

BACKGROUND: Gluten contamination in gluten-free products cannot totally be avoided. The safe threshold for gluten remains obscure. AIM: The purpose was to estimate a reasonable limit for residual gluten, based on current literature and measurement of gluten in gluten-free products on the market.
METHODS: The gluten content of 59 naturally gluten-free and 24 wheat starch-based gluten-free products were analysed by enzyme-linked immunosorbent assay. The daily intake of flours was calculated in 76 adults on gluten-free diet, and the intake compared with mucosal histology.
RESULTS: A number of both naturally gluten-free (13 of 59) and wheat starch-based gluten-free (11 of 24) products contained gluten from 20 to 200 ppm (=mg/kg). The median daily flour consumption was 80 g (range: 10-300). Within these limits, the long-term mucosal recovery was good.
CONCLUSIONS: The threshold for gluten-contamination can safely be set at 100 ppm. Provided that the daily flour intake is even 300 g, a level of 100 ppm results in 30 mg of gluten intake. This has been shown to be safe, when correlated to histology, in clinical and challenge studies. The level can be achieved by the industry, and does not make the diet too cumbersome.