Impact of new diagnostic criteria for diabetes on different populations

OBJECTIVE - For epidemiological purposes, it has now been recommended that a fasting plasma glucose value of 7.0 mmol/l can be used to diagnose diabet es, instead of a 2-h value of 11.1 mmol/l. This study assesses the impact o f making this change on the prevalence of diabetes and on the phenotype of individuals identified. RESEARCH DESIGN AND METHODS - Data were collated from nine population-based southern hemisphere studies in which a 75-g oral glucose tolerance test wa s performed. Comparisons were made between the prevalence derived from fast ing values only and the prevalence derived from 2-h values only. Cardiovasc ular risk was assessed in all individuals. RESULTS - There were 20,624 subjects in the nine surveys, of whom 1,036 had previously diagnosed diabetes and 1,714 had newly diagnosed diabetes, acco rding to either fasting or 2-h glucose. The differences in prevalence withi n each population resulting from changing the diagnostic criteria ranged fr om +30 to -19% (relative difference) and +4.1 percentage points to -2.8 per centage points (absolute difference). BMI was the most important determinan t of disagreement in classification. A total of 31% of those individuals wh o were diabetic on the fasting value were not diabetic on the 2-h value, an d 32% of those with diabetes on the 2-h value were not diabetic on the fast ing value. Apart from obesity, there were no differences in cardiovascular risk between those identified by the fasting and the 2-h values. CONCLUSIONS - Changing the diagnostic criteria is likely to have variable a nd sometimes quite large effects on the prevalence of diabetes in different populations. Furthermore, the fasting criterion identifies different peopl e as being diabetic than those identified by the 2-h criterion.