Average blood glucose vs HbA1C

HbA1c depends on average blood glucose concentration and red blood cell (RBC) lifespan. Sickle-cell anaemia and other haemoglobinopathies such as hereditary spherocytosis and G6PD deficiency reduce RBC lifespan and hence can artificially lower HbA1c levels.

Average glucose levels are likely to be more accurate as they are calculate from more data over longer period of time