Higher HbA1c and/or glucose levels alter the association patterns between glycated hemoglobin and fasting glucose levels.

•The correlations between HbA1c and glucose (FPG) was evaluated in 14,249 Chinese.•FPG positively associated with HbA1c in subjects with HbA1c < 6.5% and FPG < 7.0 mM.•High FPG/HbA1c increased the association B in subjects with HbA1c ≥ 6.5% and FPG ≥ 7.0 mM.•FPG negatively associated with HbA1c in males with HbA1c ≥ 6.5% and FPG < 7.0 mM.•No correlation was found in males and females with HbA1c < 6.5% and FPG ≥ 7.0 mM.