HbA1c Blood Test: Procedure, Normal levels and its Limitations

HbA1c also is known as glycosylated, or glycated hemoglobin, is a form of hemoglobin that is bound to glucose.

Updated: February 16, 2018


HbA1c also is known as glycosylated, or glycated hemoglobin, is a form of hemoglobin that is bound to glucose. Blood glucose levels over the past eight to twelve weeks are measured in this test. This test do not reflect daily ups and downs of blood glucose. The blood test for HbA1c level is routinely performed in people with type 1 and type 2 diabetes mellitus as this is helps to determine how well a type 1 or type 2 diabetes treatment plan including medications, exercise, or dietary changes is working. The normal range for level for hemoglobin A1c is less than 6%. Higher the HbA1c levels, poorer is the control of diabetes.

What is HbA1c?

The amount of haemoglobin, the oxygen-carrying protein in red blood cells bonded with glucose in the bloodstream is HbA1c. The bonding with glucose is called glycation.
About 90% of hemoglobin is hemoglobin A where A stands for adult type. About 8% of hemoglobin A is made up of minor components that are chemically slightly different. These minor components include hemoglobin A1c, A1b, A1a1, and A1a2. Hemoglobin A1c (HbA1c) is a minor component of hemoglobin to which glucose is bound. Sometimes HbA1c also referred to as glycated, glycosylated hemoglobin, or glycohemoglobin.

How HbA1c test is done?

A blood sample will be taken from the arm of the patient to measure HbA1c level. As HbA1c is not affected by short-term fluctuations in blood glucose concentrations caused by eating anything, fasting for the blood test is not necessary. Blood can be drawn for HbA1c testing regardless of when food was eaten. Red blood cells exist in the body for around 3 months. Therefore an HbA1c levels generally reflects blood glucose levels over the previous 8 to 12 weeks. Higher the blood glucose levels of a person, the higher the number of red blood cells that will become glycated, and therefore the higher HbA1c level they will have.

What are the levels of HbA1c?

The HbA1c level is less than 6% in a healthy person. The A1C level below 5.7 is considered as normal. If the level is 5.7% to 6.4%, then it is considered as prediabetes where as 6.5% or greater is diagnosed as diabetes. The complications of diabetes can be delayed or prevented if the HbA1c level can be kept below 7%. The aim of treatment plan of diabetes is to keep the HbA1c level as close to normal as possible of an individual. HbA1c levels can be correlated with the average blood sugar level. For example, a HbA1c measurement of 7% corresponds to an estimated average glucose of 154 mg/dl.
HbA1cmmol/mol%
NormalBelow 42 mmol/molBelow 6%
Prediabetes42 to 47 mmol/mol6% to 6.4%
Diabetesgreater then 47 mmol/molgreater then 6.4%

HbA1c chart

What are the limitations to measuring HbA1c?

HbA1c test is not useful in monitoring day-to-day blood glucose concentrations as it is not influenced by daily fluctuations in blood glucose concentration. Therefore neither it can be used for adjusting insulin doses nor can it detect the day-to-day presence or absence of hyperglycemia or hypoglycemia. HbA1c may be increased falsely in certain medical conditions such as kidney failure, high levels of triglyceride or excessive intake of alcohol. The levels may be decreased falsely in case of sickle cell disease, acute or chronic blood loss or thalassemia. Being pregnant or having an uncommon form of hemoglobin can also result in an inaccurate HbA1c level. Therefore HbA1c is not used to diagnose gestational diabetes. In such cases an oral glucose tolerance test is used.

How can you lower HbA1c levels?

HbA1c test is useful in indicating how well the blood glucose level has been controlled in past two to three months and may be used to monitor the effects of diet, exercise, and drug therapy on blood glucose in people with type 1 and type 2 diabetes. A normal or only slightly elevated HbA1c level is an indication that your diabetes is under good control. If your HbA1c level is higher then normal, you can follow your type 1 or type 2 diabetes management plan which include dietary modifications, physical activity, medications or a combination of these to lower HbA1c levels. It is recommended to change your treatment plan if your HbA1c level remains high despite following your treatment plan.

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