GLYCATED HEMOGLOBIN(HbA1C)

• HbA₁C or glycated hemoglobin is a derivative formed when adult hemoglobin(protein) reacts spontaneously with glucose(a reducing sugar)

• There are different types of glycated hemoglobin molecules, all are together called HbA₁ fraction

In HbA₁ fraction -

• 80% molecules are HbA₁C - glucose is attached to N-terminal valine of beta polypeptide of the hemoglobin molecule
• HbA₁A₁ - fructose 1.6 bisphosphate is attached to valine
• HbA₁A₂ - glucose 6 phosphates are attached to n terminal valine
• HbA₁D - glucose is attached to the lysine residue of alpha or beta chain.

• Non-enzymatic addition of aldehyde of glucose to the N-terminal valine of beta polypeptide of hemoglobin molecule to form keto amine.
• In general, the concentration of hba1c in the blood is very low, contributing to 5% of total hemoglobin but when the blood glucose concentration is more as see in diabetes the hba1c concentration is more.
• The increased concentration of glucose increases the formation of HbA₁C.
• As the average life span of RBC(red blood cell) is 120 days the hba1c concentration at any point of time reflects the average blood glucose level over the previous 2-3 months, therefore measuring hba1c provides the clinician the average picture of patients blood glucose concentration over the past 3 months.
• For long term diabetes, blood control monitoring HbA₁C is a more reliable method than random blood glucose.

FACTORS DETERMINING THE GLYCATED HEMOGLOBIN LEVELS ARE

• Average glucose concentration
• The lifespan of red blood cells
• If the life span of RBC is decreased in diseases like in hemoglobinopathies, the hemoglobin will have less time to become glycated and therefore the HbA₁C level will be less.
• Maintaining the HbA₁C to an average of <7% reduces the microvascular complications of diabetes like retinopathy, neuropathy, etc.

METHODS OF ASSESSMENT OF HbA₁C :

1.     Ion exchange high-performance liquid chromatography,

2.     Boronate affinity chromatography

3.     Immunoassay

4.     Enzymatic assays

· A common method of estimating HbA₁C concentration in POCT is based on latex immnuoagglutination inhibition methodology.

·   In this method of POCT, HbA₁C concentration and total hemoglobin concentration are measured and the ratio is reported as percent hba1c.

INTERPRETATION OF HbA₁C:

• <5.5% - Normal/Very good control
• 7% - Adequate control
• 8% - Inadequate control
• 9% - Very poor control

·   The value of HbA₁C increases by 0.1% with an increase every 10 years of age so values in the elderly differ from young adults.

ADVANTAGES :

• A fasting blood sample is not required.
• There is low intraindividual variability
• Sample is stable
• Value os not altered by acute factors
• Provides an estimate of long term blood glucose control
•  Better index for predicting complications.