definition and diagnosis of diabetes mellitus and intermediate hyperglycemia
Report of a WHO/IDF Consultation
Diabetes is a condition primarily defined by the level of hyperglycaemia giving rise to risk of microvascular
damage (retinopathy, nephropathy and neuropathy). It is associated with reduced life expectancy, significant morbidity due to specific diabetes related microvascular complications, increased risk of macrovascular complications (ischaemic heart disease, stroke and peripheral vascular disease), and diminished quality of life. P. 5
Other
considerations also impact on how a diagnosis of diabetes should be made. Does diabetes represent the upper end of a continuous distribution of glucose or a discrete entity? While hyperglycaemia is an important prognostic parameter, is it the central or most important feature determining prognosis in people with hyperglycaemia? In terms of screening asymptomatic people, how can we best balance the medical, social and economic benefits and costs?
In the review of the evidence to prepare this report, attempts to find data which examined the relationship between plasma glucose and biopsy proven diabetic renal disease were unsuccessful. Studies which have examined the relationship between plasma glucose and the less specific marker of diabetic renal disease, proteinuria, have reported some association but not as strong as with retinopathy13. Numerous studies have examined the relationship between plasma glucose and mortality and cardiovascular complications but have failed to show a definite threshold which could be used to define diabetes (see Issues 2–4 below).
The difficulty with defining normality mirrors that of defining diagnostic cut-points for intermediate hyperglycaemia i.e. placing a specific cutpoint on a continuous variable. Furthermore other factors such as age, gender and ethnicity are relevant to defining normality. Also, as data from new outcomes studies become available, what is considered normal may change. P.13.
Levitan et al22 performed a meta-analysis of thirty eight prospective studies and confirmed that hyperglycaemia in the non-diabetic range was associated with increased risk of fatal and non-fatal cardiovascular disease,
with a similar relationship between events and each of fasting and 2–h plasma glucose. From twelve studies reporting fasting plasma glucose levels and six studies reporting post-challenge glucose, cardiovascular
events appeared to increase in a linear fashion with 2–h post-challenge plasma glucose in the range below levels diagnostic of diabetes without a threshold, whereas for fasting plasma glucose there was a possible threshold at 5.5mmol/l. p. 14. Levitan EB, Song Y, Ford ES, Liu S. Is nondiabetic hyperglycemia a risk factor for cardiovascular disease? A meta-analysis of prospective studies. JAMA 2005; 293: 194-202.
23. Balkau B, Bertrais S, Ducimetiere P, Eschwege E. Is there a glycemic threshold for mortality risk? Diabetes Care 1999; 22: 696–699.
24. DECODE Study Group. Is the current definition for diabetes relevant to mortality risk from all causes and cardiovascular and non-cardiovascular diseases? Diabetes Care 2003; 26: 688–696.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC478551/ Article on hazard ratio.