Haemoglobin A1C (HbA1c) test and its significance in Diabetes
What is HbA1c?
Haemoglobin A1C is a blood test that helps the doctor estimate average blood sugar level for the past 2 to 3 months. Other commonly used names for Haemoglobin A1c are: Glycated Haemoblobin, HbA1c, or simply A1c.
It is important not to confuse HbA1c with tests with similar names such as HbsAg. HbsAg is an entirely different test related to Hepatitis B and has nothing to do with Diabetes.
HbA1C was originally used to check whether diabetes treatment is working the right way or not. These days, it is being used for screening of Diabetes also.
HbA1c and significance
a.) Screening for Diabetes: If HbA1c test is done to screen or diagnose diabetes, the following holds good as long as the test is done in a reliable lab using the correct scientific methodology.
- 6.5 or higher: probably means ‘having diabetes’. It is worth checking with Oral Glucose Tolerance test after assessing for any symptoms of Diabetes. Oral Glucose Tolerance Test or simply OGTT involves testing for Fasting Glucose and 2 hour glucose after ingesting 75 grams of Glucose.
- 5.7 and 6.4: ‘at risk of developing diabetes’. This status is called with different names such as Pre-Diabetes, Impaired Fasting Glucose (IFG), Impaired Glucose Tolerance (IGT). In such a case, it is important to change lifestyle, i.e dietary changes and also do regular exercise. It is important to lose weight if overweight. Such measures will slow the progression to Diabetes.
b.) Monitoring for Glucose control in a Diabetes patient: Significance of HbA1c test result when done to assess if current Diabetes treatments are working, i.e., to check if Glucose is under control. The target HbA1c varies from patient to patient. It is not appropriate to give a common target HbA1C value for all Diabetes patients. This is because of the differences between Diabetes patients in their age, duration of Diabetes, symptoms, co-morbidities such as heart disease and other complications such as Neuropathy, Nephropathy, Retinopathy. In general a value of 7 or less is advocated. But as detailed already, an individual target will be decided by the specialist based on the individual person’s circumstances.
Frequency of HbA1c Testing
This depends on whether one has Diabetes already and what the last HbA1C test showed.
a.) Screening for Diabetes:
- If HbA1C test was done to check for Diabetes and less than 5.7, the person tested does not have Diabetes or Pre-Diabetes. The individual needs to continue to lead a healthy life style. The individual can have annual screening or more frequently if circumstances change, for instance if the person develops symptoms of Diabetes.
- If HbA1C test was done to check for diabetes and between 5.7 and 6.4, this means the individual does not have diabetes but at risk for it. HbA1C test needs to be done at least every year, earlier if there are any symptoms of Diabetes.
b.) Monitoring for Glucose control in a Diabetes patient:
- If one has Diabetes and HbA1c is within the individual’s target range, the person should have HbA1C tests at least every 6 months.
- If one has Diabetes and recently changed treatment or if HbA1c is not in the target range, the individual should have HbA1C test every 3 months.
Why is HbA1c needed when we already have Fasting and ‘Post lunch’ Glucose test results?
This is a common question asked by patients. While Fasting and Post Lunch blood Glucose are useful, they are just a snap shot of the patient’s blood glucose at that particular instance. On the contrary, HbA1c depicts the last 2 to 3 month average blood glucose. Hence, the reason why we need HbA1c and not just fasting and ‘Post Lunch’ Glucose readings. Moreover, studies have shown that HbA1c test reflects risk of developing complications like heart attacks, brain stroke more reliably than plain glucose values alone.
If one has fasting and ‘post lunch’ glucose results in the target range, it might not necessarily mean that the overall average glucose control is good as we do not know the HbA1c value. Similarly, if a Diabetes patient comes to the clinic with Fasting and ‘Post lunch’ results above the target range, it does not necessarily mean than the average Glucose control is poor unless we know the HbA1C result.
But, there are a few circumstances such as having abnormal Haemoglobins, Anaemia, recent blood transfusion etc which can make HbA1c less reliable as a marker of one’s average glucose control.
Dr Ravi Shankar,
Consultant Endocrinologist, Apollo Hospital, Jubilee Hills Hyderabad