More than a million people in the UK have type 2 diabetes, and the number could reach 3 million by 2010. Renal (kidney) failure is one of the most serious complications of this condition. Currently, 10 per cent of adults with renal failure have diabetes, and diabetes is the single most common cause of renal failure.
Damage to the kidneys progresses slowly. It becomes apparent when protein (primarily albumin) is excreted in the urine. In its early stages, this condition is known as microalbuminuria; more severe kidney damage, revealed by higher levels of protein in the urine, is described as proteinuria. Epidemiological studies suggest that about 25 per cent of people with type 2 diabetes have microalbuminuria, and a further 15 per cent have proteinuria.
From the patient's perspective, there may be no specific symptoms until the kidneys are close to the point of failure.
But there is a marked rise in the risk of death: people with diabetes and microalbuminuria are twice as likely to die as those with normal urinary albumin levels, and the risk rises to five, or even up to eight, times more than normal with proteinuria. Most of these deaths are attributed to cardiovascular disease.
There are many factors in a patient's susceptibility to renal complications. It is much more common among people of Asian or Afro-Caribbean origin and among close relatives of patients with diabetic renal disease. In addition, poor control of diabetes and high blood pressure are associated with increased risk.
Detection of diabetic renal disease depends on urine tests.
Some of these are suitable for near-patient testing (sideroom tests). But of these, only Albustix and Albym are currently available for NHS prescription. There is no evidence to suggest that one is more useful than the other, but neither test detects microalbuminuria reliably or is sufficiently accurate for a single result to guide clinical decisions.
More accurate tests require sophisticated laboratory equipment, but even with these a single result should not be regarded as reliable because albumin excretion varies from day to day. Health professionals should therefore use these tests regularly and repeatedly; they should not rely on a single side-room test.
Management of early renal disease Diabetic renal disease develops particularly rapidly in patients with high blood pressure, and can itself increase blood pressure. Antihypertensive drugs are the most important means of dealing with the problem.
One group of antihypertensive agents - known as ACE inhibitors - has attracted particular attention.
A substantial and consistent body of evidence, including some large randomised controlled trials with follow-up periods as long as a decade, shows that these drugs can reduce the rate of progression of renal disease.
They appear to offer particular benefits for people with diabetes and albuminuria - even those who have normal blood pressure. For patients who have high blood pressure but no signs of renal disease, other antihypertensive drugs may be equally effective.
Tight control of blood glucose is another important aspect of management and reduces the risk of complications of diabetes generally.
Just under two-thirds of people with type 2 diabetes have their renal function tested annually.
Audit data from 47 districts of the UK reveals that 64 per cent (range 19.9-96.2 per cent) of patients had this test in 1998.
Cost-effectiveness Prevention of renal complications of diabetes by tight control of blood pressure is highly cost-effective. Figures calculated from a large UK trial (UKPDS) comparing tight with less tight blood pressure control show that the incremental cost per life year gained (using 1997 values) was£720 when costs and effects were discounted at 6 per cent a year.
Tight blood pressure control reduced the rate of hospitalisation, which offset the costs of antihypertensive drugs. This appears to be considerably more cost-effective than either treatment to reduce cholesterol levels, or lifestyle advice on reducing cardiovascular risk.
A US study which modelled alternative management strategies found that it was more cost-effective to treat all middle-aged people with diabetes with ACE inhibitors than to offer selective treatment after screening.
Implications of research evidence The urine of people with type 2 diabetes should be tested regularly (at least annually) for proteinuria, and if this is negative, for microalbuminuria. Two or more measurements should be carried out.
The blood pressure of people with diabetes should be checked regularly. Treatment should be offered if it is consistently above 140/90.
Treatment with ACE inhibitors is appropriate for people with microalbuminuria or proteinuria, even if their blood pressure is normal. Treatment of other cardiovascular risk factors should also be considered.
Blood glucose levels should be kept as near normal as is consistent with an acceptable quality of life.
Further research is required to establish the optimum level of dietary protein for people with type 2 diabetes and renal complications.
Promotion of self-management People with type 2 diabetes have to take active roles in managing their condition. While medical interventions are important, long-term outcomes depend on choices that they make about diet, physical activity and other health-related behaviour.
These choices will, in part, reflect knowledge about their condition and their ability to monitor it. Specific interventions to promote appropriate self-management might therefore be helpful. But how good is the evidence that they are effective?
The interventions considered in the Effective Health Care bullet in were generally provided in addition to the information sharing that should be an integral part of patient care. They fell into three broad categories: information and skills training, cognitive-behavioural modification, and patient empowerment.
The review found that many programmes produce desirable outcomes in the short term.
These included improved knowledge, weight loss and reduced blood glucose (HbA1c) levels.
Such changes need to be sustained over longer time periods to produce health gains, but there is not yet reliable evidence that this occurs. The long-term benefits of such interventions have not been demonstrated.
Educational interventions People with type 2 diabetes should be actively encouraged to be involved in their own care.
Interventions should be appropriate to the individual characteristics of people with type 2 diabetes and should take into account factors such as age, education and ethnic origin.
Further research is needed to show whether interventions to promote self-management of type 2 diabetes produce clinically significant long-term benefits.
Trials should measure morbidity, mortality and quality of life, not just 'surrogate' outcomes such as blood glucose levels or HbA1c.
Effective Health Care is an independent report based on systematic reviews of the research evidence, produced by the NHS centre for reviews and dissemination, at York University. The bullet in aims to provide NHS decision makers with information on the effectiveness of interventions and the delivery and organisation of healthcare.
For more information, phone 01904-433648 or email firstname.lastname@example.org
Effective Health Care is at www.york.ac.uk/inst/crd/ehcb.htm
1 Complications of diabetes: renal disease and promotion of self-management. Effective Health Care 2000; 6 (1).
Arabella Melville, is an independent consultant.
Rachel Richardson and Deborah Lister-Sharp are research fellows at the NHS centre for reviews and dissemination, York University