Standardization of methods and reporting in diabetes epidemiology promotes comparison between studies and may permit the pooling of results from different studies   1   2 . Standardized criteria for detecting and reporting glucose intolerance have evolved greatly since the 1960s   3 .

In the late 1970s both the US National Diabetes Data Group (NDDG) and the World Health Organization (WHO) produced new criteria on which to diagnose diabetes mellitus. In 1985, WHO modified their criteria to be more consistent with NDDG values. More recently, the American Diabetes Association (ADA)   4  and WHO   5  have produced new recommendations for the diagnosis of diabetes. The major change recommended is the lowering of the diagnostic value of the fasting plasma glucose concentration to 7.0 mmol/l. For glucose tested in whole blood, the new recommended threshold is 6.1 mmol/l   5 .

In many population studies, individuals have been categorized as having diabetes mellitus based on blood glucose values measured after an overnight fast and/or two hours after a 75g oral glucose load. Whilst WHO still recommends the oral glucose tolerance test (OGTT) as being the single best choice, they also state that “if it is not possible to perform the OGTT (e.g. for logistical or economic reasons), the fasting plasma glucose alone may be used for epidemiological purposes”   5 .

It is important to realize that different screening and diagnostic criteria may have been used for different studies in this report. The impact that the recent diagnostic cut-off level changes have on prevalence estimates seems to vary from country to country   6 . In this section, the criteria used will be reported when they are known.