It is important to monitor diabetic patients to identify those at risk of developing conditions associated with diabetes such as neuropathy, cardiovascular disease and retinopathy. Many diabetic patients have routine tests, which monitor glucose status and renal function, and are usually performed, at regular intervals. The Diabetes Complications and Control trial (DCCT) found that tight control of glucose and glycated haemoglobin (HbA1c) over a defined period of time can help to prevent these complications associated with the disease.
One of the main blood tests for the long-term status of glucose control is HbA1c, also known as glycated haemoglobin. Haemoglobin consists of four protein chains that contain four haem portions and is found abundantly in erythrocytes. The main function of haemoglobin is to transport oxygen and carbon dioxide around the body in the blood. Glycation of haemoglobin is the addition of a sugar residue to the amino groups of proteins. Adult haemoglobin usually consists of HbA, HbA2 and HbF. HbA1c is formed by the condensation of glucose with the N-terminal valine residue of each of the β-chain of HbA, this then forms what is termed an unstable Schiff base. The Schiff base is able to dissociate or undergo an Amadori rearrangement to produce the stable form, HbA1c. HbA1c is the major fraction of HbA1 and constitutes approximately 80%.
Formation of glycated haemoglobin is irreversible; the concentrations in the blood depend greatly on the life span of red blood cells and the concentration of glucose in the blood. The glycated haemoglobin represents the glucose values over the preceding 6-8 weeks. HbA1c is termed as a long-term indicator of diabetic control whereas glucose is only a short-term indicator. The interpretation of HbA1c results depends largely on the life span of the red blood cells; diseases such as haemolytic anaemia and blood loss can produce falsely low results due to the short half-life and the depleted supply of red blood cells.
The upper limit of the reference range in a non-diabetic population is 6.1% by the DCCT units, for the IFCC units this equates to 43mmol/mol.The reference ranges suggested for HBA1c analysis refer to if the patient has good to poor glycaemic control and the ranges quoted are:-
|DCCT (%)||IFCC (mmol/mol)|
- 2-5ml of blood collected into an EDTA
- Three patient identifiers from
- N.H.S. number
- Unit Number