What is glycosylated hemoglobin or HbA1c?

HbA1c or glycosylated hemoglobin is a minor fraction of total hemoglobin content or our blood, present in diabetics and non diabetics, alike. In diabetics, the fraction (or %) of HbA1c in total hemoglobin is higher, since there is more blood glucose available to glycosylate (bind with) the hemoglobin

HbA1c in monitoring diabetes

Long term control of blood sugar levels in diabetic patients is checked by testing HbA1c (glycosylated hemoglobin) level in blood, which correlates with average blood sugar levels over past 2-3 months. In fact, this is the gold standard for monitoring control of blood sugar in diabetics

Good  HbA1c level for most diabetics is 6.5% or less but for diabetics of long disease history a level of 7% is acceptable

Diabetics should get there HbA1c done at least once in six months, till the time it stays below 6.5-7%. If it is higher than that, you may need more stringent control and monitoring

To know more, read:

How often should one monitor blood glucose levels in diabetes?’

HbA1c in diagnosis of diabetes and prediabetes

HbA1c can be used to diagnose diabetes but the diagnosis should be confirmed with a repeat HbA1c test or by fasting blood sugar levels

A diagnosis of diabetes can be made if the HbA1c level is ≥6.5%. Levels  just below 6.5% indicate the presence of impaired glucose metabolism, also called prediabetes. ADA has suggested HbA1c values between 5.7 – 6.4% as the range for prediabetes, whereas WHO’s suggests levels between 6.0 and 6.5% for diagnosis of prediabetes

The prediabetics are at particularly high risk of developing diabetes and they should opt for diabetes prevention interventions

Limitations of HbA1c

However, there are some factors which limit the use of HbA1c for either diagnosis or management of diabetes. These factors are all related to conditions which affect the RBC life span or hemoglobin levels/types.

Some of these conditions such as iron deficiency anemia, active blood loss or sickle cell anemia etc. are very common in Indians and these cases HbA1c levels will not correlate with average blood sugar levels over past 2-3 months

Some  of  the factors  that  influence HbA1c levels

1. Conditions affecting RBC generation/synthesis in body

Increased HbA1c: iron, vitamin B12 deficiency

Decreased HbA1c: iron, vitamin B12 supplements, chronic liver disease

2.  Altered Haemoglobin or hemoglobnopathies

Genetic or chemical alterations in haemoglobin: sickle cell anaemia, thallasemia etc.

3. Glycation

Increased HbA1c: alcoholism, chronic renal failure

Decreased HbA1c: aspirin, vitamin C and E supplements

4.  Erythrocyte destruction

Increased HbA1c: increased erythrocyte life span: Splenectomy.

Decreased A1c: decreased erythrocyte life span:  haemoglobinopathies, splenomegaly,

rheumatoid arthritis or drugs such as antiretrovirals, ribavirin and dapsone

5. Assays

Increased HbA1c: Jaundice,  alcoholism,  chronic opiate use

Decreased HbA1c: increased triglyceride level in blood

Good standards for HbA1c testing labs

International standardization protocols have been defined for correct testing of HbA1c in blood. The most widely accepted ones are National Glycohemoglobin Standardization Program (NGSP) and the International Federation of Clinical Chemists (IFCC). So make sure that your lab follows these standards

If you take all precautions HbA1c is your biggest friend in keeping tab on your diabetes,use it well !

CHECK OUT:  Our references for diabetes mellitus