The hen's egg SPT results of discordant children (with lower duck egg SPT by definition) were spread across a range from 3 mm to 8 mm and were not limited to lower values for hen's egg SPT. Duck egg SPT may be a marker of duck egg tolerance in our cohort and after further study could be used as a guide to the introduction of duck egg into the diet. This is the first report to describe duck egg tolerance in hen's egg allergic children.