What is HbA1c?

Glycosylated haemoglobin (HbA1c), refers to the glucose in the blood that enters the human bloodstream, it combines with haemoglobin in the red blood cells, and eventually forms glycated haemoglobin. And once glucose and haemoglobin are combined, they do not separate easily until the red blood cells die.

Since the life span of blood red blood cells is less than 120 days, glycated haemoglobin responds to the average value of blood glucose over the past 2-3 months, when the higher the concentration of glucose in the blood, the higher the value of glycated haemoglobin will be.

The non-enzymatic reaction for the formation of glycated haemoglobin is continuous, slow and irreversible. The level of glycated haemoglobin is determined by past rather than immediate blood glucose concentration.

It is generally accepted that the glycated haemoglobin concentration can effectively reflect the average blood glucose level in the past 8 to 12 weeks.

Clinical application of HbA1c

Glycated haemoglobin is elevated in people with poor glycaemic control and correlates with the degree and duration of elevated blood glucose. Since red blood cells have a lifespan of about 120 days in the blood circulation, glycated haemoglobin reflects the patient's average glucose level over 8-12 weeks.Keeping glycated haemoglobin below 7% is now considered a criterion for adequate glycaemic control.

Specific clinical applications of HbA1c are shown below:

① Glycated haemoglobin is used to assess a patient's average blood glucose level over a 2-3 month period: HbA1c is more stable and accurately reflects the degree of longer-term glycaemic control, independent of occasional increases or decreases in blood glucose.

② Glycosylated haemoglobin levels can be used as a diagnostic test for diabetes：Glycosylated haemoglobin≥6.5% can be used to confirm a diagnosis of diabetes mellitus.

③ Glycated haemoglobin is used to predict the risk of developing chronic complications of diabetes: the higher the glycated haemoglobin, the greater the risk of complications. HbA1c is the gold standard for diabetes control.

④ For evaluating the effectiveness of treatment regimens in glycaemic control: HbA1c is a sensitive indicator of glycaemic control in diabetic patients and is used not only as a diagnostic but also as a key indicator for clinical follow-up.

Factors affecting HbA1c

1. Increased HbA1c levels may be due to:

Iron/vitamin B12 deficiency

Alcoholism

Chronic renal failure

Hyperbilirubinaemia, aminoglycated haemoglobin

2. Decreased HbA1c levels may be due to:

Splenomegaly, rheumatoid arthritis

Drug effect

(Aspirin, vitamin C and vitamin E)

Summary

Glycated haemoglobin is valuable for monitoring the level of glycaemic control, diagnosing and monitoring diabetes mellitus and assessing the prognosis of its complications, as well as evaluating diabetes mellitus treatment regimens.

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References

[1] A. Pazin-Filho, A. Kottgen, A. G. Bertoni, S. D. Russell, E. Selvin, W. D. Rosamond, J. Coresh. HbA1c as a risk factor for heart failure in persons with diabetes: the Atherosclerosis Risk in Communities (ARIC) study[J]. Diabetologia. 2008 (12)

[2] Eduardo G. Camargo, Renata O. Pedrini, Jorge L. Gross, Joiza L. Camargo, Sandra P. Silveiro. Lack of interference of aspirin in HbA1C measured by ion-exchange HPLC in type 2 diabetic patients: A randomized, double-blind, placebo-controlled study[J]. Clinica Chimica Acta. 2008 (1)

[3] R. C. Sundaram, N. Selvaraj, G. Vijayan, Z. Bobby, A. Hamide, N. Rattina Dasse. Increased plasma malondialdehyde and fructosamine in iron deficiency anemia: Effect of treatment[J]. Biomedicine & Pharmacotherapy. 2007 (10)

[4] Joíza L. Camargo, Jonathas Stifft, Jorge L. Gross. The effect of aspirin and vitamins C and E on HbA1c assays[J]. Clinica Chimica Acta. 2006 (1)

[5] S. Manley, W. G. John, S. Marshall. Introduction of IFCC reference method for calibration of HbA1c: implications for clinical care[J]. Diabetic Medicine. 2004 (7)

[6] Qing Qiao, Jacqueline M Dekker, Femmie de Vegt, Giel Nijpels, Aulikki Nissinen, Coen D. A Stehouwer, Lex M Bouter, Robert J Heine, Jaakko Tuomilehto. Two prospective studies found that elevated 2-hr glucose predicted male mortality independent of fasting glucose and HbA1C[J]. Journal of Clinical Epidemiology. 2004 (6)