Why there is dual reporting of HbA1c results?
The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has established a new reference measurement system for the worldwide standardisation of HbA1c. It 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.
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. For a period of time, the HbA1c (IFCC, mmol/mol) result will be accompanied by the familiar, traditional HbA1c as a percentage (also known as DCCT %) result, i.e. dual reporting. For example, a HbA1c report might read as follows: HbA1c (IFCC) 53 mmol/mol; HbA1c (DCCT) 7.0%.
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
Małgorzata Koperska, MD, writing for www.omnicalculator.com explains: “The international standard way of measuring blood glucose levels is in terms of a molar concentration, measured in mmol/L (millimoles per litre; or millimolar, mM for short). In the United States, and continental Europe mass concentration is predominantly measured in mg/dL (milligrams per decilitre).
“In contrast, mg/dL gives the concentration by the ratio of weight to volume, in this case milligrams per decilitre. mmol/L is the most common measurement used in the UK with mg/dL predominantly used in the USA and continental Europe. Blood glucose typically varies from 4 mmol/L to 6 mmol/L for people without diabetes. There are two manners of presenting the concentration of glucose in the blood.
The international standard way of measuring blood glucose levels is in terms of a molar concentration, measured in mmol/L (millimoles per litre; or millimolar, mM for short). In the United States, and continental Europe mass concentration is predominantly measured in mg/dL (milligrams per decilitre). The conversion between the glucose units is on the fact that 1 mmol/L = 18 mg/dL, but calculating that in your head can be a challenge. There are reference tables to assist with converting one to the other. Print reference table new measurements
HbA1c reporting always begs the question, can you put a single valuation number on a complex variable? The short answer is ‘no’, but to date there was only HbA1c to go on.
*DCCT Diabetes Control and Complications Trial was conducted by the United States National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) that was published in the New England Journal of Medicine in 1993. It was as a landmark study at the time, and significantly changed the management of all forms of diabetes.
** The United Kingdom Prospective Diabetes Study (UKPDS) was a clinical study published in The Lancet in 1998.
Both trials linked good control to a reduced risk of long-term complications and the unit of measurement for control was the HbA1c test.