The incidence of diabetes among 0–34 year olds in Sweden: new data and better methods

AIMS/HYPOTHESIS: We reassessed the validity of previously reported incidence rates for type 1 diabetes in 0–34 year olds in Sweden. We estimated new incidence rates through three nationwide registers. METHODS: We used capture–recapture methods to assess ascertainment in the Diabetes Incidence Study in Sweden (DISS) and estimated incidence rates in the 20–34 year age group for 2007–2009. We examined whether incidence rates in patients aged 34 and younger could be estimated through the Prescribed Drug Register (PDR) via a proxy for diagnosis of type 1 diabetes; men with at least one and women with at least three prescriptions for insulin were included if they had not been given oral glucose-lowering drugs. We scrutinised the proxy by comparing incidence rates in patients aged 14 and younger with the Swedish Childhood Diabetes Register (SCDR), which has 95–99% ascertainment, and by assessing diabetes type among 18–34 year olds in the National Diabetes Register (NDR). RESULTS: Incidence rates were two to three times higher than previously reported. The absolute number of cases (2007–2009, age 20–34) was 435 in the DISS, 923 in the NDR, 1,217 in the PDR, 1,431 in all three and 1,617 per the capture–recapture method. Ascertainment in the DISS was ~29% for 2007–2009. The proxy diagnosis in the PDR was highly reliable, while the capture–recapture method presumably generated an overestimate. CONCLUSIONS/INTERPRETATION: The incidence of type 1 diabetes in patients aged 34 and younger was two to three times higher than previously reported. The PDR can be used to reliably assess incidence rates in this age group. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00125-014-3225-9) contains peer-reviewed but unedited supplementary material, which is available to authorised users.