Definition, prevalence, prognosis, and etiology of undiagnosed type 2 diabetes. Narrative review with national and international data

Background: Although there are no recent studies on undiagnosed diabetes mellitus (UDM) in Germany, the International Diabetes Federation estimates that more than one million people aged 20-79 years are affected. Objective: Definition, prevalence, prognosis, and causes of UDM are explained and recommendations to reduce UDM are given. Materials and methods: The current literature is discussed. Results: The prevalence of UDM is highly dependent on the definition used and is lower if, for example, a second test is required to confirm the first test result. There are no recent data on the prevalence of UDM in Germany. According to older data from the Robert Koch Institute, the prevalence of UDM was 2.0% in 2008/2011. People with UDM have a higher risk of microvascular and macrovascular disease, cancer and premature death than people with prediabetes or normal glucose tolerance. Factors associated with underdiagnosis of type 2 diabetes include living alone and infrequent use of healthcare services. In addition, studies show that people who already have UDM think their own chances of developing diabetes are low. Opportunistic screening is promising to reduce UDM, for example in hospital patients over 50 years or in dental patients with periodontitis. Conclusion: In view of the increased risk of mortality and complications in UDM, people with a previous diagnosis of diabetes should, in cases of doubt, be asked more specifically whether they are aware of the diagnosis. Opportunistic screening should be carried out in people without a diagnosis of diabetes but with an unfavorable risk profile.