Fasting Plasma Glucose or HbA1c to Define Treatment and Risk Factors

In men, FPG definitions yielded more incident cases of diabetes than HbA_1c definitions, in contrast with women….

This study was done to compare incidences and risk factors for diabetes using seven definitions, with combinations of pharmacological treatment, fasting plasma glucose (FPG) ≥7.0 mmol/L, and HbA_1c ≥6.5%. Participants aged 30-65 years from the Data from an Epidemiological Study on the Insulin Resistance Syndrome cohort were followed for 9 years.

The results showed that more men had incident diabetes as defined by FPG ≥7.0 mmol/L and/or treatment than by HbA_1c ≥6.5% and/or treatment: 7.5% (140/1,867) and 5.3%, respectively (P < 0.009); for women incidences were similar: 3.2% (63/1,958) and 3.4%. Known risk factors predicted diabetes for almost all definitions. Among those with incident diabetes by FPG alone versus HbA_1c alone, there were more men (78 vs. 35%), case patients were 8 years younger, and fewer were alcohol abstainers (12 vs. 35%) (all P < 0.005). A diabetes risk score discriminated well between those with and without incident diabetes for all definitions.

From the results it was concluded that, the age profile of HbA1c and FPG differed for men and women, with FPG always higher in men, whereas HbA1c was higher in younger men but identical in the oldest age range, 60–65 years. For men only, the incidence of diabetes was lower for diabetes defined by HbA1c rather than by FPG. There has been little discussion in the literature on the differences between men and women for either FPG or HbA1c. For the incident diabetic case patients diagnosed by treatment, the classic risk factors for diabetes were mainly higher than for other definitions — age, diabetes in the family, adiposity, hypertension, with smoking and alcohol  drinking in men. This is probably because of the general practitioner recognizing these as risk factors and screening for diabetes, subsequently diagnosing and treating the patient.

Hypertension and lipid treatment were risk factors with high odds ratios in those who had incident diabetes by treatment, probably for the same reason. For the definitions of diabetes with FPG there were more men, case patients were younger, and fewer were alcohol abstainers than for definitions with HbA1c. Despite this, the diabetes risk score discriminated well for all definitions of diabetes, best for diabetes defined by treatment and worst for diabetes defined by FPG alone, but all AROCs were over 0.74. In Inter99, the cross-sectional profiles were similar for those screened diabetic only by HbA1c and only by FPG and 2-h plasma glucose (7); however, diabetes prevalence was higher when screened by HbA1c, in contrast with our incidence study. Mean HbA1c in Inter99 appears higher than in other cohorts, and this is probably the reason for the observed difference. Differences in men and women were not studied in Inter99. Because blood was only sampled at one time point to evaluate FPG and HbA1c, this study is limited to diabetes screening — not diagnosis.

Diabetes Care February 23, 2011 DC_101581