What are the traditional HbA1c units and why change?
Traditionally HbA1c was reported as a percentage of total haemoglobin. The International Federation of Clinical Chemistry and Laboratory Medicine(IFCC) has established a new reference measurement system for the worldwide standardisation of HbA1c.
The IFCC recommends that HbA1c concentration be reported in mmol of HbA1c per mol of haemoglobin (mmol/mol).
This will make comparing HbA1c results from different laboratories and clinical research trials throughout the world much easier. These developments are supported by the international diabetes organisations and came about because the HbA1c assay systems used in both the DCCT and UKPDS trials were not specific for HbA1c and were not calibrated in the manner that is now required.
What are the IFCC units and how will HbA1c be reported?
The IFCC has recommended that “HbA1c” is the official test name for what has been in the past referred to as glycohaemoglobin, A1c and the unit for reporting HbA1c concentration is mmol/mol. The range of HbA1c values for people without diabetes will be 20 to 42 mmol/mol.
The HbA1c values will be higher in people with diabetes depending on their degree of glycaemic or blood glucose control.
For a period of time, the HbA1c (IFCC, mmol/mol) result will be accompanied by the familiar HbA1c (DCCT,%) result. This is called dual reporting.
For example a HbA1c report might read as follows:
HbA1c (IFCC) 53 mmol/mol
Ref. Interval (20 - 42)
HbA1c (DCCT) 7.0 %
Ref. Interval (4.0 – 6.0)
The fact that the IFCC number is higher than the DCCT number does not mean there has been more glucose in an individual’s blood or that the diabetes was more poorly controlled. It is just a different way of expressing the same level of diabetes control. The IFCC HbA1c values are very different from blood glucose concentration values and this should reduce the risk of people with diabetes confusing both these results.
| HbA1c (DCCT) (%) |
HbA1c (IFCC) (mmol/mol) |
|---|---|
| 6.0 | 42 |
| 6.5 | 48 |
| 7.0 | 53 |
| 7.5 | 59 |
| 8.0 | 64 |
| 8.5 | 69 |
| 9.0 | 75 |
Diagnosis of diabetes
Do NOT use HBA1c for the Dx of Type 1 diabetes
Type 1
Diagnosed with elevated glucose (random > 11.1 mmol/l or fasting > 7.0 mmol/l in clinical setting (polydipsia, polyuria, wt loss ± ketonuria).
Type 2
| Symptomatic (e.g. polyuria, polydipsia, unexplained weight loss) |
Asymptomatic |
|---|---|
| A single fasting plasma glucose ≥7 OR A single random plasma glucose ≥11.1 |
A fasting glucose ≥7 on two separate occasions OR A random glucose ≥11.1 on two separate occasions OR An HbA1c ≥6.5% (48mmol/mol) on two separate occasions OR An HbA1c ≥6.5% AND a single elevated plasma glucose (fasting ≥7 or random ≥11.1) |
| Impaired fasting glucose | Pre-diabetes | Impaired glucose tolerance |
|---|---|---|
| Fasting plasma glucose 6.1–6.9mmol/l (WHO criteria) |
HbA1c 6–6.4% (42–47mmol/mol) |
Fasting plasma glucose <7.0mmol/l AND 2h plasma glucose (after 75g oral glucose load) 7.8–11mmol/l (WHO criteria) Condensed GTT in pregnancy (where HbA1c is inaccurate) |