A GP has developed a way to find up to 500,000 people with potential diabetes who risk being overlooked by their doctors.
Software highlights abnormal blood sugar tests
Simple software can highlight those whose abnormal blood sugar tests have not yet been followed up.
Dr Tim Holt, who led the project, even found six patients who had been missed at his own practice, the British Journal of General Practice reported.
Diabetes UK said early diagnosis was vital to limit diabetes-related damage.
The government is currently looking at ways to increase the amount of health screening carried out at GP practices.
However, the study suggested that blood tests of thousands of patients showing signs of early type II diabetes were already available to doctors - but not being followed up.
The computer software developed by Dr Holt, from the University of Warwick, and colleagues at Nottingham University, looked for patients who had undergone a blood test more than a year ago, and shown some hint of raised blood sugar levels, but who had not been seen by their doctor with diabetes in mind.
In a sample of 3.6 million anonymised records taken from the database at the university, they found almost 33,000 with "borderline" results which would normally require a re-test, and 3,700 whose results suggested more strongly they had undiagnosed diabetes.
If every practice in the country was using the system, said Dr Holt, he would expect to see half a million "possibles" and 60,000 "probables". He said: "The study demonstrates the power of information technology to assist practice teams in the early detection of diabetes.
"There are lots of reasons why a raised blood sugar level might not be followed up.
"For example, the doctor might be investigating another problem, and order blood tests for something else, with the 'glucose' box ticked as well.
"The patient, also might think that a note from the surgery asking them to come in about their raised blood glucose level was unimportant compared with their other problem."
Dr Holt tried the system at his own surgery in Warwickshire, and identified six patients who might be developing the condition. One of them, Peter Alexander, was diagnosed, and now has his diabetes under control.
"I wish that this system had been introduced nationwide much earlier," he said.
The charity Diabetes UK has been calling for more screening for type II diabetes, and said it was vital that patients were caught before the symptoms of the disease became apparent.
Its chief executive Douglas Smallwood said: "Diabetes is a serious condition which can lead to devastating complications such as blindness, amputations, heart and kidney disease.
"The earlier people are diagnosed, the earlier they can get on with managing the condition and reduce their risk of developing complications."
"Identifying people at higher risk of Type 2 diabetes is also a massive step forward. In many cases, leading a healthy lifestyle and managing weight can prevent or delay onset of the condition, so targeting these people is vital."
The largest GP computer software supplier, EMIS, has already installed the software into all the GP practices it serves.