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How glycated haemoglobin is formed. Source: Lehninger Principles of Biochemistry, 6th edition

Understanding Glycated Haemoglobin (HBA1c) and Blood Sugar Levels.

The amount of glycated haemoglobin in your blood correlates with the average blood sugar levels in the last 90 to 120 days. We explain how this occurs in today’s article about understanding glycated haemoglobin and blood sugar levels.

Haemoglobin is the principal protein – found in the red blood cells that carries oxygen around the body. Glucose is the primary source of energy for the body. It circulates around the body at a concentration of about 90-120 mg/dL. High blood glucose levels are detrimental to the human body.

Left untreated, excessive blood glucose levels lead to tissue and organ damage – leading to impaired wound healing, renal failure, cardiovascular disease, and retinopathy. We screen for diabetes mellitus by measuring the blood glucose (sugar) levels either randomly or after a fasting period. We then make a diagnosis of such by measuring the glycated haemoglobin levels (HBA1c or GHB).

Glycated haemoglobin is the amount of haemoglobin that has coated glucose in the bloodstream. It reflects the mean levels of blood sugar over the past 90-120 days – as a percentage. It is so because the average lifespan of a red blood cell is 120 days – after which the spleen disintegrates it to various products.

Blood glucose constantly interacts with the haemoglobin molecule through transport proteins in the red cell membranes that ensure an all-time state of equilibrium between the glucose inside the cells (intracellular) and outside the cells (plasma glucose). Because haemoglobin has a constant exposure to glucose at all ranges of concentration, glucose frequently coats it through a nonenzymatic reaction between glucose and the primary amino groups in haemoglobin. The reaction occurs at a rate that is proportional to the glucose concentration. It becomes the basis for determining the mean blood glucose levels over time.

Normally, about 5% of the total haemoglobin coats glucose molecules. It corresponds to about 120mg of glucose per decilitre of blood. The values can be as high as 13% (about 300mg/dL) in people with untreated diabetes mellitus.

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During the process of glycation, various advanced glycation end products form – which may leave the red blood cell and attach to many critical proteins within the bloodstream – which can impede such proteins from performing their normal functions. The end products may distort the integral architecture of vital organs like the kidneys and blood vessels.

Glycated haemoglobin is such an important indicator of blood glucose levels that the Diabetes Control and Complications Trial showed that its level is both an indicator of retinopathy and its progression among patients with diabetes mellitus. We use it among people with diabetes to ascertain the target range of their blood glucose levels over time.

We measure the glycated haemoglobin level by measuring the HBA1c – as a point of care (POC), STAT test or through the laboratory. It is worth noting that POC and STAT test results are usually lower than laboratory values by 0.5%.

In conclusion, it’s paramount that you understand the relationship between haemoglobin and blood glucose to enable a follow-up on diabetic patients or even diagnose diabetes early enough before complications set in. multiple laboratories countrywide perform the HBA1c assay.

Lehninger Principles of Biochemistry, 6th edition and Eyth E, Nalk R’s StatPearls about HbA1c were extremely useful writing this article.


Dr A. M. Ssekandi is a medical officer, researcher, content creator, author, and founder of He does private practice with a public touch. He is a certified digital marketer. He has earned certificates in Understanding Clinical Research and Writing in Sciences from the University of Cape Town and Stanford University respectively. He also has a certificate of Good Clinical Practice from

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