Less than a third of people with diabetes receive all the recommended regular tests, a national audit shows.
Blood glucose is just one of a raft of tests for diabetic patients
The latest figures from the NHS Information Centre show children and the elderly in England are least likely to get the care they need.
And four in five children with the condition have higher blood glucose levels than recommended, putting them at risk of complications in later life.
But diabetes care is still improving year on year, the report found.
An estimated 2.35 million people in England have diabetes and almost 10% of NHS budget is spent on the condition and its complications.
According to the 2005-06 audit of 656,000 people with diabetes, only 30% are having all of the recommended tests and measurements carried out, although this has increased over the past three years.
However, four in five are now routinely having their blood glucose level checked, up 7% from the previous year.
And there has been a 10% increase in the number of people having foot examinations - which detect signs of nerve damage and problems caused by poor circulation.
However, just over a third of people still have blood glucose levels above what is recommended.
Over a long period of time, this puts them at increased risk of developing diabetic complications, such as blindness and heart and kidney failure.
Diabetes UK said children and young people were faring particularly badly.
The audit shows that 83% of children and young people are not achieving recommended blood glucose levels of 7.5%.
And almost a third have blood glucose levels above 9.5% - a level which, according to NICE, poses a real risk to health and should attract extra resources for care
Dr Jonathan Boyce from the Healthcare Commission said: "It is good to see the number of people with diabetes receiving key measurement tests such as cholesterol levels and blood pressure is increasing and that in certain groups, the positive outcomes of those tests is also increasing.
"However, health services must not become complacent - the number of people receiving key tests still needs to rise."
Douglas Smallwood, chief executive of Diabetes UK, said it was "absolutely disgraceful" that four out of five children and young people are struggling to reach target blood glucose levels.
"Good blood glucose control is the cornerstone of diabetes management, which can help reduce the risk of diabetic complications.
"An overburdened NHS already spends £5 billion of its annual budget on treating long-term diabetic complications."
Dr Sue Roberts, national clinical director for diabetes said: "We will continue to encourage the whole of the diabetes community to engage with the audit, and to use the information it provides to commission services effectively to achieve the best outcomes for people with diabetes."