A quarter of all people who have diabetes remain undiagnosed, leaving them at serious risk of developing serious complications. The findings come from the largest ever UK clinical audit of diabetes care, carried out by the Health and Social Care Information Centre on behalf of the Healthcare Commission.

In one of the largest audits of its kind ever carried out in the UK, information about more than 250,000 people in England has been collected. The Healthcare Commission will be surveying 150,000 people with diabetes in spring 2006.

The audit compared the number of people diagnosed and registered with diabetes against the diabetes population prevalence model developed by Yorkshire and Humber Public Health Observatory.

Practices were asked whether everyone with diabetes is diagnosed and recorded in a practice diabetes register. People with diabetes were asked what is the annual rate of specific complications. Other questions focused on what proportion of people with diabetes receive the key processes of diabetes care? and what proportions of people with diabetes achieve treatment targets?

Early findings suggest that almost half of women with diabetes may be diagnosed, and that less than 50% of diagnosed people are receiving eye examinations putting them at risk of avoidable blindness.

Only 56% of people with diabetes were found to be managing their glucose levels within the levels set by NICE (HbA1c less than 7.5%).

According to the Information Centre the report highlights the need for further work to determine whether there is a systematic under-identification of women aged 40 and above. It also recommends that problems with recording of ethnictity are addressed due to the known increased risk of diabetes for particular ethnic groups.

Some 20% of PCTs, over 1,700 individual GP practices, 47 hospital trusts and 58 specialist paediatric units have already registered during the early phases of the trial with more expected to join over the coming year.

Anna Walker, chief executive of the Healthcare Commission said: "This work shows the value of national audit and we are anticipating that all PCTs will participate in the audit next year. We expect to see changes as a result of this work and we will be using participation in the audit as part of our annual performance ratings for PCTs."

Douglas Smallwood, chief executive at Diabetes UK said: "The longer people are left undiagnosed or are not managing their diabetes, the greater the risk of long term complications such as heart and kidney disease, blindness and amputations. The importance of this audit is that gaps are now identified and action can now be taken by healthcare professionals to improve services."

The ongoing audit forms part of a set of clinical audits designed to monitor care and assure consistent quality across the country.

A full copy of the report is available online.