Hemoglobin A1c (HbA1c) is glycated hemoglobin, which forms when hemoglobin within red blood cells joins with glucose. HbA1c levels reflect the average blood glucose level during the preceding 2 - 3 months. This differs from a blood glucose test, which measures the concentration of glucose at only the point at which the blood sample was collected.
- Blood glucose is constantly fluctuating depending on what and when you ate, and your activity levels. HbA1c maintains a more stable level to provide a more accurate reflection of your average glucose levels for the pervious 2 - 3 months.
- No prolonged period of dietary restriction is required for HbA1c testing. An oral glucose tolerance test requires a strict diet three days prior to testing.
- Rapid sample collection for HbA1c testing, requiring only a sample of blood. An oral glucose tolerance test requires a two hour absorption time after ingestion of a measured amount of glucose.
- The samples for HbA1c testing can be taken at any time of day or night.
- Better sample stability, as the protein analyzed in HbA1c testing is capable of remaining stable for over a week if kept refrigerated.
HbA1c levels are decreased in cases of shortened red blood cell survival, including due to haemolytic anemia, sickle cell disorders, pregnancy, and significant blood loss. Hence, the HbA1c assay cannot be used to diagnose diabetes in individuals from each of these categories.