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Saturday, May 27, 2017



Table of contents:

 General Introduction to Hb A1c
 Test Significance of HbA1c
 Clinical Significance of HbA1c
 Conditions That Affect HbA1c Concentration.
 Results Interpetation

General Introduction

Glycosylated-Haemogblobin is blood glucose bound to hemoglobin (Hb) and includes the forms of Hb A1a, Hb A1b, Hb A1c.

Glycoheamoglobin  (Hb A1c) is one of the types of minor haemoglobins found in every individual. It consists of 4-6% of the total Hb. Others make up the remaining 2-4% of the total (Phosphorylated glucose (HbA1a) or fructose (Hb A1b).

Haemoglobin A, undergoes change or glycosylation  to hemoglobin A1a,  A1b, A1c by a slow non-enzymatic process within the red blood cells during their circulating life span of 120 days.

The amount of glycosylated hemoglobin found and stored in erythrocytes depends on the amount of glucose available.

Since glycohemoglobins circulate within red blood cells whose life span lasts up to 120 days, they generally reflect the state of glycemia over the preceeding 8-12 weeks, thereby providing an improved method of assessing diabetic control.

In diabetics with hyperglycemia, the increase in G-Hb is usually caused by an increase in HbA1c.

Where the hyperglycemia is caused by insulin deficiency. Glucose concentration will increase and this glycosylation is irreversible.

Test Significance of HbA1c:

This test is an index of long-term glucose control.

A patient about to get tested for HbA1c. The test is independent  and not affected  by factors such as time of test, exercise, meal intake, medication, e.t.c.

- Hb A1c provides vital information about the success of treatment of diabetes such as the adequacy of dietary or insulin therapy.

- Provides determination of duration of hyperglycemia in new cases of juvenile onset diabetes with acute ketoacidosis.

- It also provides a sensitive estimate of glucose imbalance in mild cases of diabetes.

- It provides an evaluation of old and new forms of therapy such as oral hypoglycemic agents and single or multiple insulin injections.

- Those with Unstable day to day glucose estimations.

- In addition, for patients who change their usual habits and dietary lifestyle. 

In summary:

     1. HBA1c is used to help newly diagnosed diabetics determine how elevated their uncontrolled blood glucose levels had been over the last 2-3 months. 

    2. HbA1c is used to monitor the glucose control of diabetes over time.  The ultimate goal is to keep glucose levels close to the normal as possible to prevent complications arising from elevated glucose levels.

  The HbA1c test result will give a picture of the average amount of glucose in the blood over the last 2-3 months. This  provides a great help to diabetics and their doctors to know if the treatment plans and measures being taken to control the diabetes are successful or need to be adjusted or changed completely.

   The test is done several times while control is being achieved, and then at least twice a year to verify that good control is being maintained.


1.  HbA1c test is ordered when someone is suspected of having diabetes with presenting signs and symptoms in addition to increased blood glucose levels (hyperglycemia).

2.  Overweight persons with the following additional risk factors:
 a. Physical inactivity
 b. First degree relative with diabetes.
 c. Hypertension
 d. Abnormal lipid profile 
 e. Women with Polycystic ovary syndrome
 f.  History of Cardiovascular disease 

3. The American Diabetes Association (ADA) recommends to begin A1c testing for overweight or obese people at age 45. 
     If the result is normal, testing should be done/repeated at a minimum of 2years intervals with consideration of more frequent testing depending on initial results and risk status.

4. In addition, people who are not diagnosed with diabetes but are likely to be at increased risk for diabetes (prediabetes) should have A1c testing yearly.

Conditions that Might Affect HbA1c Results:

Hemolyzed specimens – Reject immediately. Or repeat sample collection.

It should not be used for diagnosis of gestational diabetes.

Diagnosis of diabetes in children and adolescence.

People who have had severe bleeding (chronic blood loss) or blood transfusions.

Diabetics with chronic kidney disease.

Falsely increased values may be due to hemodialysis,  and fetal-maternal transfusion.

People with chronic liver disease. (glucose impairment)

Those with varying degrees of anemia ( Iron-deficiency, Vit B12 deficiency and some Hb variants as in sickle cell disease or thalassemia). 

 In these cases, a fasting blood glucose (FBG) or OGTT should be used for screening or diagnosing diabetes.


A non diabetic person should have results  of <6.0% 
     (< 42 mmol/mol).

Increased risk individuals of developing diabetes in the future. HbA1c is between 6.0% to 6.4%
 (42 – 47 mmol/mol)

For diabetic patients, results are ≥ 6.5% (≥ 48mmol/mol).

As the HbA1c increases so does the risk of complications.

HbA1c can indicate people with prediabetes or diabetes as follows:

    HbA1C  mmol/mol       %
Normal            Below 42      Below 6.0
Prediabetes   42 to 47         6.0  to 6.4
Diabetes   ≥ 48         6.5% or over

HbA1c & Glucose Blood Levels:

 (%) HbA1c
                     (mmol/mol)                Ave. Blood Glucose   
13                                     119                                   18
12                                     108                                   17
11                                      97                                   15
10                                      86                                         13
9                                      75                                   12
8                                      64                                   10
7                                      53                                    8
6                                      42                                    7
5                                      31                                    5

Research has shown that people with type 2 diabetes who reduce their Hb a1c by 1 % are:

 19% less likely to suffer cataracts
16% less likely to suffer cardiac failure
 43% less likely to suffer amputation or death due to peripheral vascular disease.

A diabetic patient who has only recently come under control may still have a high concentration of glycosylated haemoglobin. But this concentration level will decline as newly formed RBCs with nearly normal GHb replace older RBCs with high concentrations of GHb.


In a bid to get the best out of diabetes management, I recommend that several glycated hemoglobin estimations be done severally (at least twice a year) in order to come up with diabetes control strategies to help achieve desired long term results.


While so much has been said about Hb A1C as a  monitoring tool, it is not a primary diagnostic tool to screen for diabetes and should not displace the importance of fasting plasma glucose and oral glucose tolerance tests (OGTT) in screening for diabetes.

Thank you for reading.

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