['To evaluate the relationship between temperature and hemoglobin A1c (HbA1c) and fasting plasma glucose (FPG) levels in Harbin of China and analyze whether these would affect diagnosis and control of diabetes.', 'Two groups were investigated: 1. Routine patients come from outpatients, 2. Research subjects including 224 healthy volunteers and 391 diabetic patients, who had 5 blood specimens collected between February and June 2010. Fasting plasma glucose and hemoglobin A1c were detected.', 'In non-diabetic patients, mean HbA1c concentrations for all temperature categories were not significantly different, but mean FPG level was higher at cooler temperatures (p < 0.05). In the diabetic group, mean HbA1c concentrations were higher at cool temperatures than at very cold temperatures (p < 0.05), but mean FPG level was higher at cold temperature than at other temperature categories (p < 0.05). Both the within- and the between-subject coefficients of variation (CVs) for HbA1c were smaller than for FPG.'] Is circannual temperature-related variation in hemoglobin A1c unlikely to affect its use as a diagnostic test for type 2 diabetes?