Criteria for diagnosis of DM, IFG, IGT

Diabetes is a state of chronic hyperglycaemia. Historically, its diagnosis was based upon high blood glucose in the presence of typical symptoms, but there was uncertainty as to the definition and management of asymptomatic hyperglycaemia. The 1980 & 1985 WHO expert committees identified the OGTT as the diagnostic gold standard for diabetes. Since most new cases have unequivocally raised random glucse levels, the OGTT was mainly useful in cases of doubt and for epidemiological studies. The glucose range intermediate between diabetes and non-diabetes was now called impaired glucose tolerance (IGT), and recognised as a risk factor for both diabetes and cardiovascular disease (CVD). The definition was extended in 1997 to include fasting glucose measurement, and the intermediate range was now called impaired fasting glucose (IFG). Glycated haemoglobin (HbA1c) was subsequently introduced as an alternative criterion for diabetes or impaired glucose regulation. The current criteria for the diagnosis of diabetes mellitus and the pre-diabetic states such as Impaired Fasting Glucose (IFG) and Impaired Glucose Tolerance (IGT) were set by an International Expert Committee in 2009.

Diabetes mellitus

For the diagnosis of diabetes, the current criteria are:

Measure Cut off mmol/l Cut off mg/dl
Fasting Plasma Glucose (FPG) >= 7.0 126
2 hour glucose after OGTT >= 11.1 200
Random plasma glucose >= 11.1 200*
HbA1c >= 6.5%

*diagnostic in patients with typical symptoms, perform further tests if asymptomatic

It should be noted that each of these criteria identifies a slightly different set of people as having diabetes. Thus, a person meeting the FPG criterion for diabetes will not necessarily also meet the HbA1c criterion. Generally speaking, the glucose following an OGTT seems to classify the largest percentage of people as having diabetes (4.9% of the population in the NHANES Cohort) and HbA1c the smallest (1.6% in NHANES).

Pre-diabetic states

It is well recognized that people at risk for type 2 diabetes already have higher glucose levels prior to the development of overt diabetes. And while the development of diabetes is not inevitable during these pre-diabetic stages, the risk of developing diabetes is greatly increased. These states are identified by:

Measure Cut off mmol/l Cut off mg/dl
FPC >= 5.6 100
OGTT >=7.8 140
HbA1c >= 5.7

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