The HbA1c blood test or glycosylated haemoglobin is used as a general indicator of average blood sugar levels present in plasma over about 3 months. It does not indicate whether a person is insulin resistant or not, whether they have high blood sugar or low blood sugar at times, only what the long term average blood sugar level is.
It makes no differentiation between someone who has a steady blood sugar level of 5-6 mmol/L and someone who cycles constantly between hypo and hyperglycaemia going to 15 mmol/L after a meal and then crashing down to 3 mmol/L or less soon afterwards, the latter being a typical expression of insulin resistance. It is frequently used to monitor diabetics in addition to regular blood glucose monitoring at home, or to diagnose diabetes.
How does the HbA1c work?
- HbA1c cannot be used to diagnose insulin resistance
- Regular home monitoring of blood glucose levels is the best way to monitor for blood glucose control and to isolate instances of hypoglycaemia and hyperglycaemia
- An HbA1c test can be used to provide an average value for blood sugar levels over the preceding few weeks. If it is above 6.5%, this can justify a diagnosis of diabetes.
Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ (2008). “Translating the A1C assay into estimated average glucose values.”. Diabetes Care 31 (8): 1473–8.