The basics of HbA1c test for diabetes

The role of dietary fibre in the management of diabetes
September 7, 2019
Diabetes and Urinary Tract Infection
July 7, 2020

Regularly measuring your blood sugar values is one of the fundamental pillars of diabetes management. If you are a person living with diabetes, there are multiple always to keep a tab on your blood sugar values. Some of them include:  Self-monitoring of blood glucose (SMBG) , HbA1c, Continuous glucose monitoring (CGM), flash glucose monitoring etc.

In this article, we will understand more about HbA1c.

HbA1c has many other names such as glycohemoglobin, glycated hemoglobin, glycosylated hemoglobin, and Hemoglobin A1c.

What is HbA1c?

The hemoglobin A1c test tells you your average level of blood sugar over the past 2 to 3 months. Unlike fasting, random and post-prandial blood tests that provide blood glucose value only at a specific point in time, HbA1c provides average blood sugar level over the past 2-3 months. It is therefore considered as a more robust marker of measuring glycaemic control.

The test measures how much sugar is bound to the hemoglobin in the red blood cells. Since the red blood cells have an average lifespan of three months, the test reveals average blood glucose levels for three months.

With every one percent increase in HbA1c, the risk of various macrovascular and microvascular complications of diabetes increase. Reducing hemoglobin A1c levels as soon as possible especially after the diagnosis of type 2 diabetes results in a reduction in the diabetes-related complications, including myocardial infarction (MI) and all-cause mortality. This early reduction in the HbA1c level explains the so-called legacy effect found in the landmark UKPDS study (United Kingdom Prospective Diabetes Study) conducted on people living with type-2 diabetes.[i]

How to interpret HbA1c values?

HbA1c results are given in percentages. Typical results are below.

  • Normal: below 5.7%
  • Prediabetes: between 5.7% and 6.4
  • Diabetes:5% or higher

The estimated average glucose associated with different HbA1c values can be found in the below table:

HbA1c (%) estimated average glucose (mg/dL)
5 97
6 126
7 154
8 183
9 212
10 240
11 269
12 298
Hemoglobin A1c levels should be checked, according to the American Diabetic Association, every six months in individuals with good blood sugar control, and every three months if the person is trying to establish stable blood sugar control.

Untitled design (10)

What are the limitations of HbA1c?

The major advantage of using HbA1c is that it evens out fluctuations in glucose levels after meals and with illness – however, there are certain limitations in the use of HbA1c where a false- positive or false-negative result may be obtained. These are listed below:

  • On its own, HbA1c may not be enough to diagnose diabetes in children, young people and pregnancy, or Type 1 diabetes, because of the short duration of the illness and may give a false negative
  • The HbA1c value is dependent on the glycation of red blood cells over time. Conditions in which there is increased red blood cell destruction can lead to a falsely low HbA1c value. This includes conditions like renal anaemia, chronic haemolytic anaemia, renal dialysis, chronic malaria, acute blood loss and recent transfusion
  • The HbA1c value may be falsely low in patients with an increased red blood cell turnover, such as those treated with anti-psychotics, corticosteroids and those being managed for human immunodeficiency virus infection. Also, after splenectomy it can be falsely raised
  • Conditions that alter glycation rates can also affect the HbA1c, e.g. increased alcohol consumption leads to a falsely raised HbA1c and aspirin leads to a decreased HbA1c
  • Since the test is an average of 3 months – it does not reveal the exact fluctuations in blood glucose that could have led to hyperglycemia (high blood sugar) and hypoglycemia(low blood sugar). A person with extreme fluctuations in both directions may have the same HbA1c result as a person with a steady and stable blood glucose value. Additionally, the greatest drawback of HbA1c is that it doesn’t capture hypoglycemia, even though severely low blood sugar could be fatal

Thus, the 2017 International Consensus on the use of Continuous Glucose Monitoring (CGM) convened an international panel of experts to address this issue. They suggested several key metrics such as glucose variability, glycemic variability and most importantly, time in range to address the issue.

Time in Range (TIR) readings can be defined as the time period during which glucose values within a particular acceptable range.


People with diabetes should keep a close tab on their HbA1c values and should try to keep it below 7 or the goal decided by their doctor. A combination of diet, exercise, and medication can help in bringing HbA1c levels down.


(Dr Syed Iftikhar Ali is a doctor by profession. He completed his MBBS from King George Medical University, Lucknow and his MS in general surgery from Jhansi Medical College in 2013. He has more than 7 years of work experience in the field of medicine.)


[i] King et al, Br J Clin Pharmacol 1999 Nov; 48(5): 643–648.

%d bloggers like this: