If someone is diagnosed with coeliac disease...

[NorthernDancer]

... do family members also need to be tested and if so, which ones?

Thank you

The NHS website says first degree relatives, so parent, child or siblings.

Yes it's a good idea. Quite a percentage of people are silent coeliacs, so no symptoms but still doing internal damage.

My two granddaughters were diagnosed by the age of 2. They tested their other 2 siblings but not the parents.