The guidelines have been developed by a working group supported by NHS Diabetes and the RCGP.

Research on patient records used to underpin the guidelines showed that around 40 per cent of people classified as having type-1 diabetes actually have type-2 diabetes.

In addition, around 6 per cent of those diagnosed with type-2 diabetes probably do not have the condition, the investigation suggested.

For an average-size practice this equates to about six misclassified patients and 12 patients misdiagnosed.

The working group is developing an audit tool to help practices identify patients who have been misclassified, so they can be reassessed at annual reviews.

A draft version of the criteria was unveiled at the Diabetes UK Annual Professional Conference in Liverpool last week.

As well as types 1 and 2, the guidelines include categories for genetic forms of diabetes and for patients whose classification is as yet uncertain.

To be classed as type-1, a patient must have been put on insulin immediately after diagnosis (if aged over 35 years) or within six months of diagnosis (if under 35).

The guidelines include gestational diabetes as a form of non-diabetic hyperglycaemia, alongside impaired glucose tolerance and impaired fasting glucose.

Professor Kamlesh Khunti, a GP and professor of primary care diabetes and vascular medicine at the University of Leicester, presented the guidelines at the conference.

The new criteria should be included in the QOF, he said. 'QOF is clearly wrong at the moment, in just having type-1 and type-2 diabetes,' he said.

He said it was important to be able to categorise patients as 'unknown' before deciding on a definite classification.

Professor Andrew Hattersley of Peninsula Medical School, also on the working group, said the guidelines were designed to be practical so that non-experts could use them and improve on current classification.

New Classifications
Diabetes Type-1 Type-2 Genetic Other Unknown Non-diabetic hyperglycaemia Impaired glucose tolerance/impaired fasting glucose Gestational diabetes