Impact of changing the criteria for diagnosing diabetes in Australia

To the Editor: Both the American Diabetes Association (ADA)1 and the World Health Organization (WHO)2 have lowered the fasting plasma glucose (FPG) level for the diagnosis of diabetes from 7.8 mmol/L to 7.0 mmol/L. The Australian Diabetes Society (ADS) has also adopted the lower level.3 However, these organisations differ in the procedure for diagnosis they recommend. The recent article by Hilton and colleagues4 compared these procedures, with particular attention to including an oral glucose tolerance test (OGTT). We, on the other hand, have investigated the impact of lowering the diagnostic FPG level to 7.0 mmol/L.

Data were obtained by the Geelong Osteoporosis Study from an age-stratified sample of women randomly selected from electoral rolls for the Barwon Statistical Division5 and adjusted to match the national age profile. Venous FPG level was determined after an overnight fast, together with blood pressure (BP, seated) and anthropometric measurements, in 944 women aged 20–91 years (mean age, 47.5 years; SD, 17.8 years). History of diabetes was ascertained by questionnaire.

The prevalence of self-reported diabetes and diabetes defined by an FPG level of 7.0 mmol/L or higher was 4.3% (95% CI, 3.0%–5.6%; 41 women), whereas using an FPG level of 7.8 mmol/L or higher gave a prevalence of 3.8% (95% CI, 2.6%–5.0%; 36 women). With the lower cut-off level, 29% of women (12) were unaware of their diabetes, compared with 19% (7) using the higher FPG level cut-off point.

Characteristics of those identified using the lower cut-off FPG level are shown in the Table. After age-matching all patients with diabetes with control participants, diabetes was significantly associated with obesity (body mass index, > 30; odds ratio [OR], 4.2; 95% CI, 1.5–11.6) and central body fat distribution (waist/hip ratio, > 0.8; OR, 8.0; 95% CI, 2.3–25.9); and non-significantly associated with higher blood pressure (systolic, > 140 mmHg; diastolic, > 85 mmHg; OR, 2.0; 95% CI, 0.8–4.9).

The new criterion for diagnosing diabetes identifies a subgroup of the population with a high proportion of obesity and android habitus, with a tendency to higher blood pressure. The recommendation of lowering the diagnostic FPG level increases the prevalence of diabetes by an apparently small proportion, but would diagnose diabetes in an additional 34 000 women in Australia.