Glucose sticks to the out side of the cells, which last about 6 weeks. The HbA1c test tests how much glucose is stuck to your haemoglobin and this gives you an indication of how much has stuck in the last 6 weeks, which gives a rough idea of how your diabetes control has been.bA1c is a test that measures the amount of glycosylated hemoglobin in your blood. The test gives a good estimate of how well diabetes is being managed over time.