IDF diabetes Atlas: Global estimates of undiagnosed diabetes in adults for 2021

To provide up-to-date estimates of undiagnosed diabetes mellitus (UDM) prevalence - both globally, and by region/country, for the year 2021.Data sources reporting diabetes prevalence were identified through a systematic search in the peer-reviewed and grey literature. The prevalence of undiagnosed diabetes was estimated from the data from each country where data was available. For countries without in-country data, the prevalence of undiagnosed diabetes was approximated by extrapolating the average of the estimates from countries with data sources within the same International Diabetes Federation (IDF) region and World Bank income grouping. We then applied these stratified prevalence estimates of UDM from each country to the number of adults in each strata and summed the counts to generate the number of adults with UDM (aged 20-79 years) for 215 countries and territories.In 2021, almost one in two adults (20-79 years old) with diabetes were unaware of their diabetes status (44.7%; 239.7 million). The highest proportions of undiagnosed diabetes (53.6%) were found in the Africa, Western Pacific (52.8%) and South-East Asia regions (51.3%), respectively. The lowest proportion of undiagnosed diabetes was observed in North America and the Caribbean (24.2%).Diabetes surveillance needs to be strengthened to reduce the prevalence of UDM, particularly in low- and middle-income countries.