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Keywords:

  • diabetes;
  • epidemiology;
  • fasting blood glucose;
  • HbA1c;
  • impaired fasting glucose

Diabet. Med. 29, 905–910 (2012)

Abstract

Aims  Using the HbA1c level to define diabetes has several advantages and these advantages also apply to define a high-risk group. However, the risk of diabetes increases as HbA1c increases and a certain degree of arbitrariness in the cut-off for the high risk group is unavoidable. The aim of this study was to determine the HbA1c cut-off for defining a high-risk group that corresponds to the fasting plasma glucose cut-off by comparing the risk of diabetes against the fasting plasma glucose and HbA1c levels in the Japanese population.

Methods  A retrospective cohort study was conducted using data from annual health examinations performed in Omiya city. A total of 11 271 subjects between the ages of 40 and 79 years without diabetes at baseline were followed for up to 7 years. According to the new diagnostic criteria, diabetes was defined as an fasting plasma glucose level ≥ 7 mmol/l or an HbA1c level ≥ 48 mmol/mol (≥ 6.5%) or a self-report. The HbA1c cut-off corresponding to the fasting plasma glucose cut-off was determined using the incidence, hazard ratio, and a receiver operating characteristic analysis.

Results  Eight hundred and sixty subjects developed diabetes. The incidence, hazard ratio, and receiver operating characteristic analysis all indicated that an HbA1c cut-off of 39 mmol/mol (5.7%) corresponded to an fasting plasma glucose level of 5.6 mmol/l.

Conclusions  Our results suggested that the HbA1c cut-off for high-risk of diabetes should be 39 mmol/mol (5.7%), consistent with the American Diabetes Association recommendation. Further research is needed to determine whether our results are applicable to other populations.