Glycated haemoglobin: the essential blood test for controlling blood sugar in diabetes
Glycated haemoglobin (HbA1c) is a blood test that measures the concentration of haemoglobin bound to glucose. It reflects the average glucose concentration (blood glucose) during the last three months and is useful for the diagnosis of diabetes and for glycaemic control in diabetic patients
Measurement of glycated haemoglobin is performed by taking a blood sample at a blood collection centre
Haemoglobin is a protein responsible for transporting oxygen inside red blood cells.
There are various types of haemoglobin, but the predominant form, approximately 95-98%, is haemoglobin A.
Glucose is the main source of energy for the cells in the body.
During digestion, carbohydrates taken in with a meal are broken down into glucose, which enters the bloodstream, raising blood glucose, which is converted into energy by the pancreas’s release of insulin, a hormone that helps glucose enter the body’s cells.
If the body is unable to produce insulin (type 1 diabetes) or there is a reduced response of the cells to its action (type 2 diabetes), blood glucose can rise to dangerous levels.
Glucose, circulating in the blood, partly binds spontaneously to haemoglobin A.
The haemoglobin molecule bound to glucose is called glycated haemoglobin
The higher the concentration of glucose in the blood, the more glycated haemoglobin is formed.
Once glucose has bound to haemoglobin, it remains there for the life of the red blood cell (approximately 120 days).
The prevalent form of glycated haemoglobin is referred to as HbA1c or A1c
HbA1c is produced daily and is slowly eliminated from the blood as older red blood cells die and are replaced by younger ones that contain very little glycated haemoglobin.
This process is completely normal and poses no danger to the patient’s health.
In fact, haemoglobin, although glycosylated, continues to perform its function, which is to transport oxygen to the tissues.
According to the American Diabetes Association, the HbA1c test can be used as an alternative to other diagnostic tests based on glucose levels (such as the oral glucose load tolerance test or fasting plasma glucose measurement) used for screening or diagnosing diabetes, or to assess the risk of developing it.
It cannot, however, be used for the diagnosis of diabetes in children and adolescents.
Glycated haemoglobin is used to assess blood glucose control in the medium and long term
It therefore suggests the risk of developing diabetes complications such as nephropathy, neuropathy and diabetic retinopathy.
The glycated haemoglobin assay should be repeated regularly in all diabetic patients to document the degree of glycaemic compensation, both in the initial assessment and to monitor therapy.
In patients with poorly compensated diabetes, measurement of glycated haemoglobin should be repeated approximately every 3-4 months.
If the situation is under control, measurement is recommended at least twice a year.
In any case, the frequency of dosing depends on the judgement of the treating physician.
The evaluation of glycated haemoglobin should not be used in screening for diabetes related to cystic fibrosis, for the diagnosis of gestational diabetes, in patients who have suffered severe haemorrhage or are suffering from renal insufficiency or liver disease, as well as people with haemoglobinopathies such as sickle cell anaemia or thalassaemia.
Fasting or following a particular diet is not required to undergo the test.
In fact, the glycated haemoglobin levels that are measured depend on the blood glucose trend in the months preceding the blood test.
Blood glucose levels in the hours immediately before the blood test do not influence the result at all.
Reference values are now expressed in millimoles (mml/mol), but many laboratories still report glycated haemoglobin values as a percentage of total haemoglobin.
The normal range is between 20 and 38 mml/mol
As a percentage, the normal range is between 4% and 6%.
For a diagnosis of diabetes, however, the value must be at least 48 mml/mol, i.e. 6.5%.
When measured for control during therapy, glycated haemoglobin should generally be kept below 53 mmol/mol equivalent to 7%.
The guidelines for the treatment of diabetes indicate that the main goal is to keep glycated haemoglobin levels no higher than 53 mmol/mol (7%), preferably below 48 mmol/mol (6.5%).
If the values are higher, it means that blood glucose over the past few months has not been well controlled.
The diabetologist will review with the family and the child the lifestyle, dietary indications and insulin dosage so that these can be discussed and appropriate changes made.
All diseases capable of causing changes in the number of circulating red blood cells, such as the increase or, conversely, the destruction of red blood cells (the cells responsible for transporting haemoglobin) can lead to alterations in glycated haemoglobin levels.
Even people with certain haemoglobinopathies such as sickle-cell anaemia or thalassaemia may therefore have unreliable glycated haemoglobin results
Conditions such as high triglycerides (hypertriglyceridemia), high bilirubin (hyperbilirubinemia), chronic aspirin intake, opiate addiction, iron deficiency anaemia, spleen removal, kidney failure and chronic alcoholism can lead to an increase in glycated haemoglobin.
A drop in glycated haemoglobin may be due to factors such as chronic and haemolytic anaemia, leukaemia and recent haemorrhage.
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