Bimodal Distribution of Glucose Is Not Universally Useful for Diagnosing Diabetes

OBJECTIVE: Bimodality in the distribution of glucose has been used to define the cut point for the diagnosis of diabetes. Previous studies on bimodality have primarily been in populations with a high prevalence of type 2 diabetes, including one study in a white Caucasian population. All studies included participants with known diabetes. The aim of this study was to assess whether a bimodal structure is a general phenomenon in fasting plasma glucose (FPG) and 2-h plasma glucose that is useful for deriving a common cut point for diabetes in populations of different origin, both including and excluding known diabetes. RESEARCH DESIGN AND METHODS: The Evaluation of Screening and Early Detection Strategies for Type 2 Diabetes and Impaired Glucose Tolerance (DETECT-2) project is an international collaboration pooling surveys from all continents. These studies include surveys in which plasma glucose was measured during an oral glucose tolerance test; in total, 43 studies (135,383 participants) from 27 countries were included. A mixture of two normal distributions was fitted to plasma glucose levels, and a cut point for normal glycemia was estimated as their intersection. In populations with a biologically meaningful cut point, bimodality was tested for significance. RESULTS: Distributions of FPG and 2-h plasma glucose did not, in general, produce bimodal structures useful for deriving cut points for diabetes. When present, the cut points produced were inconsistent over geographical regions. CONCLUSIONS: Deriving cut points for normal glycemia from distributions of FPG and 2-h plasma glucose does not appear to be suitable for defining diagnostic cut points for diabetes.