This was first adopted in June 2009. During the first two years until May 2011, results were being reported in both units as %age and mmol/mol, so as to enable health professionals and patients to get used to the new units. This was then further postponed for 6 months.
When HbA1c results are expressed as %age haemoglobin, the equation describing the relationship is:
IFCC/HbA1c (mmol/mol) = [DCCT/HbA1c %age – 2.15] × 10.929
|DCCT aligned HbA1c (%age)||New IFCC HbA1c (mmol/mol)|
In a busy diabetes clinic converting these units can be a challenge.
An easy way to get an idea of the HbA1c values is to follow the rule of 2s. For eg. 7% would be 7-2 =5 and 5-2=3: 53 mmol/mol or 9% would be 9-2=7 and 7-2=5: 75 mmol/mol.
Another useful way to remember these conversions is that 7.0% is equivalent to 53 mmol/mol. Every %age increase or decrease thereafter is equivalent to 11 mmol/mol. For eg. 8% is 64 mmol/mol and 9% is 75 mmol/mol. These methods work well for HbA1c from 4% up to 13% which is the case for the majority of patients with diabetes presenting to our clinics.
A number of international societies are moving to use HbA1c to diagnose diabetes. An HbA1c of 48 mmol/mol (6.5%) is recommended as the cut point for diagnosing diabetes. However, a value of less than 48 mmol/mol (6.5%) does not exclude diabetes diagnosed using glucose tests.
- Barth JH et al. Consensus meeting on reporting glycated haemoglobin and estimated average glucose in the UK: report to the National Director for Diabetes, Department of Health. Ann Clin Biochem 2008; 45: 343-4