Time to end navel-gazing over prediabetes

4 minute read

Research on threshold levels for a diagnosis of prediabetes has sparked fresh debate on risks and interventions


Authors of a new meta-analysis strongly support the lower US threshold for prediabetes, saying the move would reduce cardiovascular deaths.

But Australian experts dispute the need to expand the diagnosis, questioning whether a lower cut-off would be clinically useful.

The study of 1.6 million people found an impaired fasting glucose in the 5.6-6.9 mmol/L range was still associated with higher rates of cardiovascular disease, coronary heart disease, stroke and all-cause mortality.

Increases in HbA1c to 5.7-6.4% were also associated with an increased risk of cardiovascular disease and coronary heart disease.

“These results support the lower cut-off point for impaired fasting glucose according to [the American Diabetes Association] criteria as well as the incorporation of HbA1c in defining prediabetes,” the authors concluded.

The US group defines prediabetes as a fasting glucose of 5.6-6.9 mmol/L or HbA1c of 5.7-6.4%. In Australia, the RACGP cut-off is 6.5% or greater.

Only the week before the release of the meta-analysis, a paper published in the Lancet Diabetes Endocrinology found that HbA1c was the best predictor of long-term diabetes complications, and called for clear international guidelines in order to accurately target lifestyle and other interventions.

But Dr Gary Kilov, Tasmanian GP and co-author of the RACGP’s guide to type 2 diabetes management, said that worrying about the lower threshold was a debate we shouldn’t be having.

The question really is “Why are we navel gazing?” he said.

“Why are we debating whether the fluff in the navel is white or off-white? Because in effect the advice is going to be very much the same. And as you get closer to a diagnosis of diabetes, you’re going to be looking at a range of other things as to whether you might have pharmacotherapy or surgery or other interventions,” he said.

“I think there would be factors supervening your HbA1c.

“Someone who has got very high cholesterol or very high blood pressure, is really obese and their HbA1c is 6.4% – that person is going to do really well with metabolic surgery. So should everyone with prediabetes have metabolic surgery? Of course not.”

Professor Jonathan Shaw, head of Population Health Research at Baker IDI, said that evidence now suggested the risk was continuous down to levels below 5.6%.

“One of the reasons that WHO and others have not followed the ADA lead is that when the threshold drops from 6.1 to 5.6, you double or treble the size of the IFG [impaired fasting glucose] population, so you need a good reason to ‘medicalise’ such a large population group,” he said.

Professor Shaw said that currently there was no strong evidence that intervening in people with impaired fasting glucose prevented progression to diabetes, unlike the strong evidence for IGT [impaired glucose tolerance].

“So, even accepting the risk is there doesn’t mean that we should automatically change the threshold and label 10% to 20% of the population with a condition that we can’t usefully intervene on.”

Associate Professor Michael d’Emden, Queensland endocrinologist, was also sceptical of the need to lower the threshold of prediabetes.

“The question is whether there is clinical benefit of labelling these patients as ‘prediabetic’.

“Diabetes implies a risk of developing a disease associated with specific microvascular complications, and that is related to higher blood glucose with an HbA1c > 6.5%. To me, prediabetes means that they are at risk of developing diabetes,” he said.

The meta-analysis could mean mild hyperglycaemia was a marker of increased cardiovascular risk and contributed to the overall risk of CVD,  possibly prompting a clinician to treat with lifestyle changes, he said.

“In other words, what are we really meaning when we label someone with prediabetes? Should it be ‘pre-cardiovascular disease’?”

BMJ 2016; online 23 November

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