Test for Glycated Haemoglobin (HbA1c)

Dr Mayanglambam Chingkheilemba *

Haemoglobin A1c, also called glycated or glycosylated haemoglobin, is a haemoglobin with glucose attached. The HbA1c test evaluates the average amount of glucose in the blood over the last 2 to 3 months by measuring the percentage of glycated haemoglobin.

Haemoglobin is an oxygen-carrying protein found inside the red blood cells (RBCs). There are several types of normal haemoglobin, but the predominant form is haemoglobin A (about 95-98%). As glucose circulates in the blood, some of it spontaneously bind to haemoglobin A.

The higher the level of glucose in the blood, the more glycated haemoglobin is formed. Once the glucose binds to the haemoglobin, it remains there for the life of the red blood cell – normally about 120 days. The predominant form of glycated haemoglobin is referred to as A1c and this is produced on a daily basis and slowly cleared from the blood as older RBCs (with non-glycated haemoglobin) take their place.

WHY GET TESTED?

To help identify those at an increased risk of developing diabetes; to monitor the glucose control of diabetics and to aid in treatment decisions.

SAMPLE REQUIRED FOR THE TEST

A blood sample is needed.

PREPARATIONS NEEDED

No special preparation is needed for the test.

HOW IS IT USED?

The HbA1c test may be used to screen for and diagnose diabetes or risk of developing diabetes mellitus (also known as diabetes). The test is also used to monitor treatment for someone who has been diagnosed with diabetes. It helps to evaluate how well the person’s glucose levels have been controlled by treatment over time. For monitoring purposes, an A1c of less than 7% indicates good glucose control and a lower risk of diabetic complications for the majority of diabetics.

The HbA1c test, however, should not be used to screen for cystic fibrosis related diabetes or gestational diabetes in pregnant women, or for diagnosis of diabetes in children and adolescence, people who have had recent severe bleeding or blood transfusions, those with chronic kidney or liver disease, or people with blood disorders such as iron-deficiency anaemia, vitamin B12 deficiency anaemia, and some haemoglobin variants (for example, people with sickle-cell disease orthalassemia). In these cases, a fasting plasma glucose or oral glucose tolerance test should be used for screening or diagnosing diabetes.

The HbA1c test is also used to monitor the glucose control of diabetics over time. The goal of those with diabetes is to keep their blood glucose levels as close to normal as possible. This helps to minimise the complications caused by chronically elevated glucose levels, such as progressive damage to body organs like the eyes, kidneys, cardiovascular system, and the nerves. The A1c test result gives a picture of the average amount of glucose in the blood over the last 2-3 months. This can help diabetics and their healthcare providers know if the measures that are being taken to control their diabetes are being successful or need to be adjusted.

A1c is frequently used to help newly diagnosed diabetics determine how elevated their uncontrolled blood glucose levels have been over the last 2-3 months. This test may be done several times while control is being achieved, and at least twice a year to verify that good control is being maintained.

WHEN IS IT DONE?

HbA1c may be done as part of a general health check-up or when someone is suspected of having diabetes because of classical signs or symptoms of increased blood glucose levels (hyperglycaemia) such as:
o Increased thirst.
o Increased urination.
o Increased appetite.
o Fatigue.
o Blurred vision.
o Slow-healing infections.

The test may also be done in adults who are overweight with the following additional risk factors:
o Physical inactivity.
o High blood pressure (hypertension).
o First-degree relative (sibling or parent) with diabetes.
o Abnormal lipid profile.
o Women with polycystic ovary syndrome.
o History of cardiovascular diseases.
o Other clinical conditions associated with insulin resistance.

WHAT DOES THE RESULT MEAN?

In screening and diagnosis, some results that may be seen include:
o A non-diabetic person will have an A1c result less than 5.7%
o Diabetes: A1c level is 6.5% or higher.
o Increased risk of developing diabetes in the future; A1c of 5.7% to 6.4%

For monitoring glucose control, A1c is currently reported as a percentage and, for most diabetics, it is recommended that they aim to keep their haemoglobin A1c below 7%. The closer diabetics can keep their A1c to the American Diabetes Association’s (ADA) therapeutic goal of less than 7% without experiencing excessive low blood sugar (hypoglycaemia), the better their diabetes is in control. As the A1c increases, so does the risk of complications.

An individual with type 2 diabetes, however, may have an A1c goal selected by his or her healthcare provider. The goal may depend on several factors, such as length of time since diagnosis, the presence of other diseases as well as diabetes complications, risk of complications from hyperglycaemia, etc.