Associations of HbA1c and fasting plasma glucose with incident diabetes: Implications for pre-diabetes thresholds in a Japanese population.

AIMS: This study assessed pre-diabetes (pre-DM) cutoffs for HbA1c and fasting plasma glucose (FPG) that were associated with an increased risk of incident DM.

METHODS: We evaluated 2267 non-diabetic Japanese health-check examinees (HbA1c: <6.5% [<48mmol/mol] and FPG: <7.0mmol/L) who were 30-79 years old and were followed-up for 5 years. Incident DM was defined as HbA1c of ≥6.5% (≥48mmol/mol), FPG of ≥7.0mmol/L, or physician-diagnosed DM.

RESULTS: During 11047 person-years, we identified 99 incident DM cases (4.3%). The incidence of DM increased with increasing baseline HbA1c or FPG levels, and the change points (95% confidence intervals) were 5.7% (5.6-5.7%; 39mmol/mol [38-39mmol/mol]) for HbA1c and 5.5mmol/L (5.5-5.6mmol/L) for FPG. The adjusted hazard ratios (HRs) for incident DM per one standard deviation-increase in HbA1c and FPG were 5.5 (4.4-6.8) and 4.0 (3.2-4.8), respectively. The adjusted HRs for incident DM were significantly higher at HbA1c of 5.7-6.4% (39-46mmol/mol) or FPG of 5.5-6.9mmol/L, compared to HbA1c of <5.7% (<39mmol/mol) or FPG of <5.5mmol/L.

CONCLUSION: The lower cut-offs for pre-DM may be 5.7% (39mmol/mol) for HbA1c and 5.5mmol/L for FPG in this Japanese population.