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Glycated haemoglobin HbA1c in follow-up

The higher the long-term blood sugar level, the more blood sugar or glucose will attach to the haemoglobin in the blood red cells.

The relationship between HbA1c and the complications related to diabetes. Picture: Terveyskirjasto.fi

In addition to blood sugar self-monitoring and continuous glucose monitoring, long-term blood sugar balance can be assessed by measuring the glycation of red cells i.e. glycated haemoglobin HbA1c. HbA1c is determined on the basis of a laboratory blood test or using a rapid meter at the appointment 2–4 times per year.

The HbA1c test is often referred in Finnish as "pitkäsokeri" meaning "the long sugar" as a reference to a long-time blood sugar level. There is no need for fasting before the test, and it can be done at any time of the day.

The HbA1c level is the best indication of the average blood sugar balance during a period of 2–8 weeks before the sampling. When the high blood sugar balance is corrected, HbA1c will be reduced within 10–20 days.

If you have had diabetes for a longer period of time, you will likely be more familiar with seeing the result as a percentage, as in the image above. Today, instead of a percentage, the result is expressed as mmol/l.

A laboratory will give an HbA1c reference level of 20–42 mmol/mol because, without diabetes, it will remain below 42 mmol/mol, i.e. 6 percent. Some people can find it hard to distinguish between the general HbA1c target in diabetes and their personal target.

  • The general HbA1c target in diabetes treatment is below 48–53 mmol/mol depending on the person’s age, duration of illness, diabetes treatment and hypoglycaemia sensitivity.

  • The personal target is individually set together with one's own doctor.

HbA1c  %

Average blood sugar mmol/l and its 95 % variation range

HbA1c  mmol/mol


7,0 (5,5–8,5)



8,6 (6,8–10,3)



10,1 (8,1–12,1)



11,8 (9,4–13,9)



13,4 (10,7–15,7)



14,9 (12,0–17,5)



16,5 (13,3–19,3)


The general HbA1c target level of 48–53 mmol/mol is a safe level in relation to both too low and too high blood sugar levels.

In insulin therapy, a lower level brings a higher risk of too low blood sugard i.e. hypoglycaemia and a higher level brings a higher risk of related complications.

If the HbA1c level has been 64 mmol/mol (8 %) for years, the risk of related complications is 5 times higher. If the level is 86 mmol/mol (10 %), the risk of related complications is 18 times higher compared to a predominantly normal blood sugar.

Updated 30.9.2023