Type 2 diabetes is a condition characterised by raised levels of glucose in the bloodstream, and its diagnosis is generally made when blood glucose levels are higher than 11.1 mmol/l (200 mg/dL) 2 hours after a oral glucose load (of 75 g).
However, blood sugar control is a spectrum: between what are thought to be ‘healthy’ blood sugar levels and type 2 diabetes exist states which are not extreme enough to be called diabetes, but are associated with enhanced risk of developing this condition.
For example, if the glucose concentration 2 hours after the glucose load is 7.8-11.1 mmol/L (140-200 mg/dL), then a diagnosis of ‘impaired glucose tolerance’ is made. The term ‘Impaired fasting glucose’ is also used to define individuals with fasting blood glucose levels of 6.1-6.9 mmol/L (110-125 mg/dL) (according to the World Health Organization).
Another relatively newly-coined term is ‘pre-diabetes’. This diagnosis is based on a measurement known as the HbA1c which gives an indication of the overall blood sugar (glyaemic) control over the preceding 3 months or so. One of the supposed advangates of this test is that it does not require fasting nor an oral glucose load. According to the American Diabetes Association, a HbA1c of 5.7%-6.4% indicates ‘pre-diabetes’, though some bodies have recommended a slightly higher threshold for this condition. The basic thinking here is that by identifying pre-diabetes, individuals may be helped with interventions including drug therapy.
While this all may seem eminently sensible on the surface, there are a number of problems with this approach. These are explored in quite some detail in a paper published this week in the British Medical Journal co-authored by Professor John Yudkin from University College London and Professor Victor Montori from the Mayo Clinic in the US .
The article explains that the relationship between glycaemic control and health risks are a continuum, and where we begin to diagnose pre-diabetes is utterly arbitrary. If we apply the criterion recommended by the ADA, then apparently half the Chinese population (that’s almost half a billion people) have pre-diabetes. The authors question whether we even have the resources to treat vast swathes of the population according to these arbitrary criteria.
Of course a stronger case might be made for those arguing for population treatment if this had been tested. But as the authors point out, there simply is no evidence that earlier intervention based on the ADA’s criteria leads to either improved health or a reduced risk of death.
What we do know if that certain interventions appear to be able to delay the onset of diabetes by about 2-4 years. The real effects in terms of reducing healthcare costs or disease burden, though, are unknown.
And even if genuine benefits exist, let’s not forget that applying a diagnosis of ‘pre-diabetes’ to someone is not without risk. We have risks associated with medication, say, but also there may be issues with self-image, health and life insurance (particularly in the US).
One of the first-line drugs used to treat pre-diabetes is metformin. The authors point out that data suggest that using this drug may reduce the risk of developing type 2 diabetes by about 31 per cent. However, as the authors point out, what this means is that treating pre-diabetes in this way means individuals now have a “100% chance of using metformin with the goal of reducing by 31 per cent their risk of developing a condition that might require them to use metformin.”
This approach with metformin or some other drug may have some sections of the drug industry rubbing their hands with glee, I suppose, but it’s certainly true that overall benefit is not assured, and there is even considerable potential for harm.
The authors are sceptical regarding any supposed benefits, and also warn that we risk deflecting from the real issues with diabetes and pre-diabetes relating, for instance, to diet and exercise. The article ends with three points that doctors should discuss with patients. These are:
- A diagnosis of pre-diabetes does not mean that you will develop diabetes. In fact, of 100 people like you, fewer than 50 are likely to develop diabetes in the next 10 years
- There are ways of reducing your risk of developing diabetes that involve changing your diet and being active. These can result from efforts you make as well as changes in your environment (food supply, workplace conditions, education, and other social determinants of health)
- There are drugs to delay diabetes, but these are the same drugs you will need if you do develop diabetes, and the value of starting them before you have developed diabetes is unknown
The footnotes to the article state that: “The authors are clinical academics with a shared interest in patient centred diabetes care and shared decision making.” And this comes loud and clear in their article, I think. Their focus really does seem to be on taking an objective look at the data and giving patients the very best information on which a truly informed decision can be made.
The article also states that it is: “…part of a series on overdiagnosis looking at the risks and harms to patients of expanding definitions of disease and increasing use of new diagnostic technologies. The underlying message here is that more medicine is not necessarily better (and may in fact be a bad thing). We need more articles like this, and we need more high profile medical journals willing to publish them.
1. Yudkin JS, et al. The epidemic of pre-diabetes: the medicine and the politics. BMJ 2014;349:g4485