How is Diabetes Mellitus diagnosed?

In many cases of diabetes, the clinical diagnosis is obvious and the diagnosis is confirmed by a single random blood or urine glucose test. A random blood glucose level of greater than 11.1 mmol/l on two occasions or a fasting glucose levels of more than 7.0 mmol/l indicates diabetes.

The diagnosis of diabetes has been standardised by the World Health Organisation (WHO) and is based on a test of glucose tolerance. The basis of the test is to give a 75g oral dextrose load after an overnight fast. The blood glucose level is then tested two hours later, and the results are then analysed as seen below:

Blood glucose (mmol/l)


2 hours

Normal glucose tolerance (NGT)



Impaired glucose tolerance (IGT)


6.7-10.0 (11.1)

Diabetes mellitus


>10.0 (11.1)