2.3. Outcome measures
In the study area all children with T1D are diagnosed according to the standards set by the American Diabetes Association (American Diabetes Association, 2011). Since presence of islet au- toantibodies precedes manifest clinical onset of T1D, we only in- cluded control children who had not tested positive for auto- antibodies (more than one) against the 65 kD isoform of glutamic acid decarboxylase (GADA), the protein tyrosine phosphatase-re- lated IA-2 antigen (IA-2 A), insulin (IAA) and the zinc transporter 8 (ZnT8A) which could indicate early signs of disease (Regnéll and Lernmark, 2013). We used only controls who had been tested no later than 1.5 years prior to 1 May 2013.