HbA1c is a blood test that shows how your blood sugar has averaged over the past two to three months, after which the analysis is often called long-term sugar. Unlike a regular blood sugar test, HbA1c is not only affected by what you have recently eaten or drunk, but provides a more long-term picture of the body's blood sugar balance.
HbA1c is used both to detect and monitor diabetes. The test can show whether blood sugar has been elevated for a long time, even if you do not have clear symptoms. For people who already have diabetes, HbA1c is used to monitor how blood sugar has developed and assess the effect of treatment and lifestyle changes.
What does an HbA1c test show?
Glucose in the blood binds to hemoglobin, the oxygen-transporting protein in red blood cells. The higher the blood sugar has been, the more glucose is bound to the hemoglobin and the higher the HbA1c value.
Because red blood cells circulate in the blood for several months, HbA1c provides an estimate of the average blood sugar level over time. However, blood sugar in recent weeks affects the result more than levels further back.
When may it be relevant to measure HbA1c?
An HbA1c test may be relevant if you want to control your long-term sugar, have risk factors for type 2 diabetes or experience symptoms that may be linked to elevated blood sugar. The test may be relevant, for example, in the case of:
- increased thirst or the need to urinate more often than usual.
- unexplained fatigue or low energy levels.
- blurred vision.
- recurrent infections.
- slow-healing wounds.
- overweight, especially in combination with abdominal obesity.
- high blood pressure or elevated blood lipids.
- diabetes in close relatives.
- previous gestational diabetes.
- follow-up of diagnosed diabetes.
Type 2 diabetes often develops gradually and can cause few or no clear symptoms for a long time. An HbA1c test may therefore also be relevant for people who feel healthy but have an increased risk of diabetes.
How is HbA1c interpreted?
HbA1c is stated in Sweden in the unit mmol/mol. The result needs to be assessed based on the laboratory's reference range, your age, medical history and whether the sample is being taken for screening, diagnosis or follow-up of an already known diabetes.
In a person without diagnosed diabetes, an elevated HbA1c may indicate that blood sugar has been higher than normal for a longer period of time. A value below the limit for diabetes may still mean an increased risk of developing type 2 diabetes, especially if other risk factors are present.
HbA1c and the diagnosis of diabetes
An HbA1c value of 48 mmol/mol or higher can be used as a criterion for the diagnosis of type 2 diabetes in adults who are not pregnant. If there are no clear symptoms of diabetes, the result usually needs to be confirmed with a new HbA1c test or with another diagnostic glucose test.
A normal HbA1c does not always rule out diabetes. In the event of typical symptoms, suspicion of rapidly rising blood sugar or conflicting test results, the analysis may need to be supplemented with P-glucose, fasting glucose or an oral glucose load.
What does elevated long-term sugar mean?
An elevated HbA1c means that blood sugar has been higher than desirable on average over the past few months. The higher the value, the greater the likelihood of a lasting disruption in the body's regulation of blood sugar.
Long-term elevated blood sugar can damage blood vessels and nerves over time. It can increase the risk of, among other things, cardiovascular disease, kidney damage, vision damage, reduced sensation and impaired circulation. A deviating result should therefore be followed up and assessed together with other risk factors.
HbA1c in diabetes monitoring
For people with diabetes, HbA1c is a key test for monitoring long-term blood sugar control. Repeated tests can show whether dietary changes, physical activity or drug treatment have had the desired effect.
The target value is individual and can be affected by, among other things, age, type of diabetes, treatment, comorbidities and the risk of too low blood sugar. A single general target value therefore does not suit everyone, but should be determined together with the treating healthcare provider.
Do I need to fast before an HbA1c test?
You normally do not need to fast before taking an HbA1c test. The test can be taken at any time during the day and is not directly affected by the last meal. This makes HbA1c particularly useful for assessing blood sugar levels over a longer period.
When can HbA1c give a misleading result?
HbA1c is affected by the lifespan of red blood cells and can therefore in some situations give a misleading picture of blood sugar levels. The result can be affected in the following cases:
- anemia or certain forms of iron deficiency.
- increased breakdown of red blood cells.
- recent blood transfusion.
- major bleeding.
- certain hemoglobin variants.
- pregnancy.
- certain kidney or liver diseases.
HbA1c is also not the best test for suspicion of a rapid onset of diabetes, as the value changes gradually. In the event of severe thirst, large amounts of urine, rapid weight loss, nausea or clear general effects, healthcare should be contacted for urgent assessment and direct measurement of glycemia.
HbA1c and P-glucose measure different things
HbA1c shows the average blood sugar level over a longer period, while P-glucose shows the blood sugar at the time of the sample. The samples therefore complement each other and together can provide a clearer picture of the body's blood sugar regulation.
If diabetes or an abnormal HbA1c is suspected, it may be relevant to also analyze P-Glucose. For a broader assessment of the risk of type 2 diabetes and cardiovascular disease, blood fats, blood pressure and other metabolic markers may also need to be considered.
HbA1c, glucose and C-peptide complement each other
HbA1c shows how blood sugar has averaged over time and P-glucose shows blood sugar at the time of the sample. C-peptide can be used as a supplementary blood test to assess how much insulin the body produces itself.
C-peptide may be relevant in cases such as unclear diabetes type or when you want to assess the pancreas' remaining insulin production. The test should be interpreted together with a simultaneous glucose value and is not used alone to diagnose diabetes. An HbA1c test provides valuable information about your long-term sugar but cannot replace a medical assessment. An elevated or unexpected result may need to be checked with a new sample and supplemented with further analyses.
