At least 1.3 million people in the UK have diabetes. It can affect people of all ages and all ethnic groups. This first article in a three-part series provides an overview of type 1 and 2 diabetes. It explains the aetiology, signs and symptoms and how a diagnosis is reached. Risk factors and psychosocial implications are also considered.
VOL: 99, ISSUE: 01, PAGE NO: 30
Mary Burden, RGN, MPH, is consultant nurse, diabetes, Heart of Birmingham Teaching Primary Care Trust
Types of diabetes
Diabetes mellitus arises through a lack of insulin or resistance to its action. It is clinically defined by symptoms of diabetes and by measurement of fasting or random blood glucose concentration (and occasionally by glucose tolerance test). There are two principal classes of diabetes - type 1 and type 2.
1. Type 1 diabetes, also referred to as insulin-dependent diabetes mellitus because it requires the administration of insulin, is an autoimmune disease where there is destruction of the insulin-producing (beta) cells in the islets of Langerhans of the pancreas. Before the isolation of insulin in 1922, type 1 diabetes was fatal. It can occur at any age, but most often it is children who develop this type of diabetes.
2. Type 2 diabetes, also referred to as non-insulin-dependent diabetes, is caused as the result of reduced secretion of insulin and to peripheral resistance to the action of insulin; that is, the insulin in the body does not have its usual biological effect. It can often be controlled by diet and exercise when first diagnosed, but many patients require oral hypoglycaemic agents or insulin in order to maintain satisfactory glycaemic control and prevent the complications of diabetes.
The World Health Organisation’s definition of type 2 diabetes was updated in 1999 (WHO et al, 1999) after clinical practice and research found that the diagnostic level of a fasting venous plasma glucose of 7.8mmol/L was set too high and that people were experiencing the complications of diabetes at a lower level than this. The diagnosis is now made if the fasting plasma glucose (FPG) is greater than 7mmol/L on two separate occasions, unless there are definite diabetic symptoms, when only one FPG is required.
Diabetes mellitus can affect people of all ages and there are at least 1.3 million in the UK with the condition (King et al, 1998). Diabetes is increasing, not only in the UK but also worldwide. In addition, many people have type 2 diabetes but are unaware of it because they are not experiencing any symptoms, or the symptoms they do have are ascribed to ‘getting older’. Table 1 lists the common symptoms of type 1 and type 2 diabetes. As many as 50 per cent of people with type 1 diabetes do not know they have it until they present with the complications of the condition (Matthews, 1999). It is thought that, on average, people have type 2 diabetes for 6-7 years before they are diagnosed (Turner, 1998).
Type 2 diabetes
Most people with diabetes (about 85 per cent) have type 2, the number of people increasing with age and ethnicity. Ten per cent of the UK white population over the age of 65 years have type 2 diabetes (Croxson et al, 1991). The numbers are even higher in the Indo-Asian population - at least 25 per cent of over those over the age of 65 have type 2 diabetes (Costa et al, 1991). There is a high prevalence of type 2 diabetes, also, in the African-Caribbean population (Burden et al, 2000). More men than women develop type 2 diabetes (Davies et al, 1999). Social class has an impact, too, with a higher prevalence of type 2 diabetes among people living in poverty, and worse outcomes (Conolly et al, 2000).
Diagnosing and treating type 1 diabetes
In the case of a person who is ill and experiencing the signs and symptoms described in Table 1, a diagnosis of type 1 diabetes is usually made by taking a random blood glucose test. Insulin will be started immediately and the patient, and sometimes a carer, learns how to perform the task. If, for some reason the person or carer cannot manage the injections, support can be given by the district nurse.
The role of the diabetes specialist nurse is to explore different injection techniques and devices, support the patient to adjust insulin doses, encourage self-management techniques, begin the process of education about the meaning of diabetes and its consequences, and act as a resource to the patient and family and other associated healthcare professionals.
Measuring glycaemic control
Glucose attaches itself to haemoglobin in the red blood cells (glycation) - the higher the level of glucose the more there is to become attached to the cells. A red blood cell has a lifespan of about 120 days, so measuring how much glucose has glycated (HbA1c) provides a good indication of long-term (about three months) glycaemic control. The recommended target for type 1 diabetes is less than 7.5 per cent and for type 2 diabetes the target is less than 7 per cent.
Diagnosing type 2 diabetes is often more problematic. If someone is experiencing symptoms, a diagnosis can be made if a fasting plasma glucose of above 7mmol/L is recorded. If the person has no symptoms but the level of suspicion is high, at least two separate fasting plasma glucose measurements are needed. If these remain borderline, a glucose tolerance test (GTT) is required. False positives can be obtained if the carbohydrate level in the diet is reduced before the test is given and also if the person is ill. The patient should make no changes to his/her diet until tested and the test should be delayed if the person has a concurrent illness.
Since 1999 there has been an increasing interest in diagnosing impaired glucose tolerance (IGT) and impaired fasting glycaemia (IFG), rather than waiting until people become diabetic. This is because it is known that people with IGT and IFG are at increased risk of cardiovascular disease (WHO et al, 1999), and it is important to address the other risks of cardiovascular disease in this group of people. Several studies (Knowler et al, 2002; Tuomilehto, 2001) have shown that it is possible to delay or prevent the onset of diabetes if interventions are begun at the impaired stage of glucose intolerance. The Diabetes National Service Framework Standards document (DoH, 2001) includes prevention of diabetes as Standard 1. Table 2 shows the range of venous plasma glucose levels needed to diagnose normal glucose tolerance, impaired glucose tolerance, impaired fasting glycaemia and diabetes.
Young people can have type 2 diabetes, but it is much more common in the middle aged and the elderly. The insulin resistance which is characteristic of this type of diabetes occurs at different sites of the body. This can include skeletal muscle, fat cells, the liver, or all of these sites. Oral hypoglycaemic agents (OHAs) are prescribed for those with type 2 diabetes who are unable to maintain glycaemic control by diet and exercise and do not yet need insulin.
There are different types of OHAs. The sulphonylureas encourage the pancreas to secrete insulin, so will work only if there are beta cells present in the pancreas. Other types of OHAs include biguanides, post-prandial regulators and those that act on insulin resistance. Acarbose interferes with carbohydrate absorption. Metformin (a biguanide) interferes with fat absorption and hepatic gluconeogenesis ; rosiglitazone and pioglitazone have an effect on insulin resistance. In time, as the beta cells deteriorate, OHAs, even in increasing dosages and combinations, will no longer work to maintain normal blood glucose levels and insulin will be needed, either on its own or in combination with an OHA.
The role of insulin
To understand the role of insulin in diabetes it is necessary, first, to understand how glycaemic control is maintained in people who do not have diabetes. Normally, the body maintains strict glycaemic control: the normal glucose level is 4-7mmol/L in the fasting state, and even after a large meal the level will not normally go above 8mmol/L. When blood glucose levels rise in someone who does not have diabetes, the beta cells in the pancreas produce insulin, while the alpha cells there reduce the production of glucagon, a hormone that increases hepatic glucose production by stimulating gluconeogenesis (new glucose) and glycogen breakdown. Glucose is transported to the muscles, where it is stored as glycogen (stored energy). It is also stored in the liver, which stops making new glucose. As a result, blood glucose levels fall.
When blood glucose levels are low in a person who does not have diabetes, insulin production falls and glucagon production is increased. The glycogen that is stored in the liver is then converted to glucose, and the liver starts to make further glucose - neogenesis - as a consequence of which the amount of glucose sent to the muscles is reduced and the blood glucose rises.
Explaining the signs and symptoms
Understanding what happens when the body has insufficient insulin will help explain the signs and symptoms of diabetes. Without sufficient insulin, the blood glucose level in the body rises and it spills over into the urine. Renal thresholds vary between individuals and are low in some groups such as pregnant women and children but high in the elderly. The normal renal threshold for glucose is usually about 10mmol/L. In the elderly, however, blood glucose can be as high as 17mmol/L before there are any signs of glycosuria. The renal threshold can also be lower than 10mmol/L. Glycosuria is sometimes seen even if the blood glucose is normal, in which case it is called renal glycosuria.
In pregnancy, urine testing for glucose is not reliable when tight glycaemic control is essential, therefore the mother-to-be will always be asked to monitor her blood glucose levels using a glucose meter.
When there are high levels of glucose in the urine, water is taken out of the body in excessive amounts by the process of osmosis. At the same time as the glucose and water are passed, salts and minerals are lost, the lack of which can lead to the muscle cramps that people newly presenting with diabetes and those with hyperglycaemia often complain of. The excessive amount of urine that is passed leads to thirst and dehydration. Some people need to drink very frequently, while for others, the dehydration and consequent thirst may be relatively mild.
Large variations in glucose concentration result in water being attracted into the lens of the eye, the consequence of which is blurred vision. Many patients newly diagnosed with diabetes fear that this signals they are going blind, but this is not permanent and once their glucose levels have been restored to normal their vision will once again be clear.
Weight loss and tiredness are also a feature of diabetes. When little or no insulin is circulating round the body, the energy taken in as food circulates in the bloodstream because it cannot enter the body’s cells, which means that glucose levels in the body rise. When this excess glucose (energy) is excreted in the urine (glycosuria), there is consequent loss of energy. However, with the administration of insulin this process stops, energy is regained and weight loss can be restored because the body is once again able to use the energy from food.
If the glucose remains circulating in the body for some time before insulin is administered, the body starts to break down protein and fat in order to supply the energy it needs. The liver then tries to compensate for the lack of glucose entering the cells and produces new glucose by neogenesis, therefore blood glucose levels keep rising. As protein and fat are broken down, ketone bodies are formed. If this process continues, and little or no insulin is present, the patient becomes dehydrated and comatose, respirations are depressed, acidosis will develop and the patient will die.
Diabetes increases susceptibility to infections and the reasons for this are multifactorial. Because hyper-glycaemia can disrupt the action of phagocytic and other white cells, people with diabetes are immunologically suppressed, which limits the body’s ability to resist invasion by bacterial, viral and fungal agents. Infection is a major cause of hyperglycaemic crisis in people with diabetes and leads to many hospital admissions.
Anyone can develop diabetes but there are risk factors that make it more likely. Some factors are modifiable, such as being overweight, but others are not, such as a person’s family history. Type 1 diabetes can sometimes occur in families: genetic factors are thought to account for about one-third of the susceptibility towards type 1 diabetes. Despite there being a genetic link, the chances of a child developing type 1 diabetes are small (8-10 per cent).
With type 2 diabetes, however, there is often a family history of the condition. Those who are overweight and lead a sedentary lifestyle are at increased risk of developing diabetes because insulin resistance can be caused by obesity. The action of insulin is rendered more sensitive if weight is lost. Exercise and increased activity will also lead to increased sensitivity to the action of insulin. This beneficial change occurs both in people with diabetes and those without.
Women who have given birth to a large baby (> 4,500g) are at risk of diabetes later in their life, as are women who developed gestational diabetes during their pregnancy, even if they reverted to normal glucose tolerance after the baby was born. It is important to support these women after their baby is born and to encourage them to maintain ideal weight and undertake regular exercise so as to prevent diabetes occurring later.
Some people accept their diagnosis of diabetes and all that this means, and manage to adapt to their new lifestyle, but others find it difficult. Changes will need to be made to the type of food they eat, the amount they eat of particular foods and perhaps to the time at which they eat their meals. Because of the required changes to lifestyle it is not surprising that many people need some professional psychological support.
Diabetes may have an impact on people’s careers, driving, and insurance policies (life, driving, travel). Difficulties surrounding holidays, work or travel abroad may prove insurmountable without support. People with diabetes who are also caring for others, for example children or elderly relatives, may find it very difficult to put themselves first.
Some people who have been diagnosed as having diabetes feel that they have been condemned to a life where everything has to be planned. There are, however, support networks available. For example Diabetes UK, a charity that supports people with diabetes, their families and the health professionals who care for them, has local and regional branches where people can meet and discuss problems and learn from each other how they manage their day-to-day-life.
Next week: The role of the nurse in diabetes care.