Validation of HbA1c of 6.5% for Diagnosing Diabetes Mellitus via the Use of Taxometric Analysis

PurposePrevious studies in which authors examined the internal and external validity of a glycemic cut-point for diagnosis of diabetes mellitus have provided mixed results. The purpose of the current study was to test the internal validity of the HbA1c 6.5% cut-point with taxometric analysis.MethodsData on 14,798 participants were obtained from the National Health and Nutrition Examination Survey, years 1999–2008. Fasting plasma glucose and HbA1c were submitted to the taxometric procedures MAMBAC (mean above minus below a cut) and MAXSLOPE (MAXimum SLOPE). The comparison curve fit index was the outcome measure, with values less than 0.40 and greater than 0.60 indicative of dimensional and categorical solutions, respectively.ResultsIn the full sample, MAXSLOPE and MAMBAC procedures yielded CCFIs of 0.778 and 0.872, respectively. Analyses were repeated in subgroups by age, sex, fasting insulin level, ethnicity, and year; the lowest comparison curve fit index measurement from any analysis was 0.706.ConclusionsThese results support a categorical overdimensional model of diabetes, consistent with the new HbA1c cut-point recommendation.