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Limitations of HbA1c in diabetes control

The importance of the HbA1c to controlling type 2 diabetes is well understood. Haemoglobin takes time to collect glucose molecules as they do not instantly attach themselves, and so HbA1c levels are not as susceptible to daily fluctuations in blood glucose levels.

This results in a better indication of how blood glucose levels have been maintained over the previous few months.

But it is this very mechanism of binding between haemoglobin and glucose that can lead to a falsely elevated value for HbA1c investigations in certain patients. The value can also vary depending on the type of laboratory assay being used.

This phenomenon is caused by the presence and interference of haemoglobin variants and derivatives, which are typically present in patients from Asian and Afro-Caribbean origins, where unfortunately type 2 diabetes rates are now even higher than those from other ethnic backgrounds.

Measuring fructosamine level is another useful method of monitoring the effectiveness of therapy in diabetes, but unlike HbA1c, which reflects this over a period of six to eight weeks, fructosamine reflects the average blood sugar concentration over a two- to three-week period.

Thus a clinical advantage of this test is that fructosamine responds more quickly to changes in therapy, and can be a useful method of determining whether a patient is worsening or improving in the short-term.

Barry Hill is chief biomedical scientist in the haematology department of Wigan Royal Infirmary

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