Guidance note # 9
Controlled Document 337/GN9 Version 4 Prepared by: Mr Gareth Jones, Principal Biochemist
Issued April 2011. Reviewed annually. Authorised by: Dr Anne Dawnay, Consultant Biochemist
HbA1c is one of the glycated Proteins steadily become ‘glycated’, binding extra sugar from the
haemoglobins time they are made to the time they are broken down and removed.
HbA (adult haemoglobin) is one such protein and its glycated form is
called HbA1. HbA1c is one subtype with added glucose.
HbA1c ‘integrates’ a patient’s Glycation is a slow irreversible process, with the rate depending on
glucose level over time the glucose concentration and half-life of the protein. The HbA1c, as
a fraction of all HbA present, represents the average rate of
glycation over the life of HbA (about 120 days) and particularly in the
previous 6-8 weeks. This integrated view of glucose control is useful
in the long term management of people with diabetes.
New units for HbA1c have been HbA1c is now being reported in units of mmol/mol HbA as well as
introduced existing % units as part of a worldwide standardisation effort. Dual
reporting will continue until at least June 2011, after which results
will be given in new units only. Guide unit conversion table:
Old Units % (DCCT) 6.0 6.5 7.0 7.5 8.0 9.0
New Units mmol/mol 42 48 53 59 64 75
In some cases the HbA1c HbA1c will be low if red cell life is shortened (for example in
cannot be properly interpreted haemolytic and sickle cell anaemias), will be uninterpretable for a
considerable period after any blood transfusion and cannot be
reliably identified when substantial amounts of non-HbA
haemoglobin are present.
HbA1c should not be requested HbA1c should not be requested in patients with a
in patients with a known haemoglobinopathy. The HbA1c method used at UCLH detects such
patients and the sample will be reported as unsuitable.
Such patients may require haemoglobin typing (by Haematology).
Diabetes control may be assessed alternatively using serum
fructosamine, which is glycated serum protein (mainly albumin), and
reflects glycaemic control over the previous few weeks.
HbA1c as a diagnostic test HbA1c is affected by a variety of genetic, haematologic and illness-
related factors (see above). The WHO and Diabetes UK therefore
only recommend it for diagnosis when such confounders are known
to be absent. In such circumstances, two HbA1c results greater than
6.5% (48 mmol/mol) can be used to diagnose diabetes.
However values below 6.5% do not exclude diabetes. Fasting
glucose and GTT remain the primary diagnostic tests.
Testing frequency depends on Good diabetic control: Check at annual review
diabetic control Poor diabetic control: Check every 3 months
Very poor diabetic control: Check every month (as encouragement)
Pregnant diabetic control: Check every month
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