Introduction: After diabetes mellitus, thyroid diseases are the second most frequent endocrine system disorders in the general population. The most prevalent type of glycated haemoglobin is haemoglobin A1C (HbA1c). HbA1c levels are influenced by factors that affect erythrocyte turnover or survival as well as the current glycemia, leading to values of HbA1c that are artificially high or low. Both the American Diabetes Association (ADA) and the World Health Organization have approved the use of HbA1c for the detection and treatment of diabetes