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Table 1: Comparision of HbA1c units
Percentage units (%)
Molar units (mmol/mol)
6.0 42
6.5 48
7.0 53
7.5 59
8.0 64
8.5 69
9.0 75
9.5 80
10.0 86
10.5 91
11 97

Since the beginning of August 2009, general practitioners and nurses will have noticed the change to dual reporting of HbA1c results. Previously, results had only been reported in percentages (%), but now are being reported with molar units (mmol/mol) alongside (Table 1).

This practice of dual reporting will continue for two years after which time laboratories will likely only report molar units.

The reason for this change to molar units backdates to August 2007 when there was international agreement that a change in HbA1c units was needed.1

The equivalent for the current HbA1c target of 7% is a new HbA1c target of 53 mmol/mol.

There is some concern that patients or their carers may become confused with the change in reporting of their HbA1c results and that their diabetic control may deteriorate due to lack of understanding of the new molar units. It is hoped that the dual reporting system will allow time for both practitioners and their patients to become familiar with the new units, interpretation and utilisation.

Kilpatrick’s Kludge* and other conversion formulae

Kilpatrick's Kludge

An easily remembered way to approximate the conversion from % to molar units is by using “Kilpatrick’s Kludge” :2 – minus 2, minus 2.

For example: for the HbA1c result of 8%, the mmol/mol result is eight minus two (6), minus two (4) equaling 64 mmol/mol.

Diabetes UK provide the following conversion equation3 between conventional HbA1c % results and HbA1c molar units:

Type a number in either box for the equivelent to appear in the other
HbA1c mmol/mol  =  HbA1c %
HbA1c(mmol/mol)  =  (HbA1c(%) - 2.15) x 10.929

References

  1. Hicks J, Muller M, Panteghini M. Consensus statement on the worldwide standardisation of the HbA1c measurement. Diabetologia. 2007; 50:2042-3.
  2. Kilpatrick E. Changing times: International standardisation of HbA1c reporting. Journal of Diabetes Nursing. 2009; 13:199(1).
  3. Diabetes UK. National Diabetes Support team. The Association for Clinical Biochemistry. HbA1c Standardisation for Laboratory Professionals. Available from: http://www.acb.org.uk/docs/HbA1cLabProfessional.pdf. Last accessed: 17 September 2009.