Defining remission of type 2 diabetes in research studies: A systematic scoping review

Background Remission has been identified as a top priority by people with type 2 diabetes. Remission is commonly used as an outcome in research studies, however, a widely accepted definition of remission of type 2 diabetes is lacking. A report on defining remission was published (but not formally endorsed) in Diabetes care, an American Diabetes Association (ADA) journal. This Diabetes care report remains widely used. It was the first to suggest three components necessary to define the presence of remission: (1) absence of glucose-lowering treatment (2) normoglycaemia (3) for duration ≥1 year. Our aim is to systematically review how remission of type 2 diabetes has been defined by observational and interventional studies since publication of the 2009 report. Methods and Findings Four databases (MEDLINE, EMBASE, Cochrane library, CINAHL) were searched for studies published from 01.09.2009-18.07.2020 involving at least 100 participants with type 2 diabetes in their remission analysis, which examined an outcome of type 2 diabetes remission in adults >=18 years, and which had been published in English since 2009. Remission definitions were extracted and categorised by glucose lowering therapy, glycaemic thresholds and duration. 8966 titles/abstracts were screened. 178 studies (165 observational, 13 interventional) from 33 countries were included. These contributed 266 definitions of which 96 were unique. The 2009 report was referenced in 121 (45%) definitions. 247 (93%) definitions required the absence of glucoselowering therapy. 232 (87%) definitions specified numeric glycaemic thresholds. The most frequently used threshold was HbA1c<42mmol/mol (6.0%) in 47 (20%) definitions. Time was frequently omitted. 104 (39%) definitions defined time as a duration. The main limitations of this systematic review lie in the restriction to published studies written in English with sample sizes of over 100. Grey literature was not included in the search. Conclusions We found that there is substantial heterogeneity in the definition of type 2 diabetes remission in research studies published since 2009, at least partly reflecting ambiguity in the 2009 report. This complicates interpretation of previous research on remission of type 2 diabetes and the implications for people with type 2 diabetes. Any new consensus definition of remission should include unambiguous glycaemic thresholds and emphasise duration. Until an international consensus is reached, studies describing remission should clearly define all three components of remission.