HB1AC and diagnosing diabetes

Dippy3103

Well-Known Member
Messages
325
I was wondering why HB1AC isn't used as the diagnostic test for diabetes. As it reads our longer term levels surely it must be a more valid than the 'snapshot' which is what a fasting test is in essence. I was hoping someone better informed than me could explain.
Thanks in advance to anyone who can satisfy my curiosity!
 

phoenix

Expert
Messages
5,671
Type of diabetes
Type 1
Treatment type
Pump
There is an international definition of diabetes and how and what levels to diagnose it.

Under this a person with one fasting glucose test of >7mmol or a random test >11mmol and without other symptoms should be retested or have an OGTT at another time unless there is 'unequivocal hyperglycaemia with acute metabolic decompensation or obvious symptoms'. At my own diagnosis there was just one fasting test but that was over 3x the normal level and it was pretty obvious I was ill.

In their report of 1999 the World Health Org. wrote:
An alternative to blood glucose estimation or the OGTT has long been sought to simplify the diagnosis of diabetes. Glycated haemoglobin, reflecting average glycaemia over a period of weeks, was thought to provide such a test. Although in certain cases it gives equal or almost equal sensitivity and specificity to glucose measurement (6), it is not available in many parts of the world and is not well enough standardized for its use to be recommended at this time

However at the start ot his year the US diabetes association (ADA),after some research decided to change from using the WHO criteria. They switched to recommending the use of an HbA1c for diagnosis . They have set an HbA1c cut point of ≥6.5% for the diagnosis of diabetes and a level ≥6% but <6.5% to identify those at high risk for diabetes.
They also say that 6.5% shouldn't be considered an "absolute dividing line” between normal glycemia and diabetes because “glucose impairment runs on a continuum.”

Following this change, the European Association for the study of diagnosis has started considering using HbA1c and will report later this year.
Recent research from the UK shows that some people who fail a OGTT would have HbA1cs below 6.5% and so might be missed. However there are more people that would pass an OGTT but have an HbA1c above 6.5%. This means that there would be more people diagnosed (this would add to GP's workload). They also found that using the HbA1c would increase the numbers diagnosed from the South Asian community. (apparently for South Asians there would be 2.1-fold increase in detection, compared with a 1.4-fold rise in white Europeans.)