5.2 Type 1 diabetes
Type 1 diabetes was previously called insulin-dependent diabetes. This is because in people with Type 1 diabetes their pancreas fails to produce insulin and they are dependent on taking insulin for their treatment. It would be useful to look back at Figure 5 to remind yourself of the actions of insulin. As we have already discussed, without insulin glucose cannot enter tissues and cells, and so the plasma glucose level increases. When the plasma glucose level is high, glucose is passed out of the body through the kidneys in the urine. At the time of diagnosis, if the urine is tested with a urine testing stick there will be lots of glucose present, whether the patient has eaten or not. Water is required in order to excrete the glucose through the kidneys and patients often pass large amounts of urine and are therefore thirsty. Although there is plenty of glucose in the blood, because it cannot enter the tissues it cannot be used as a fuel source. Instead the body breaks down fat and protein to use as fuel. As a result, the person often loses weight very rapidly for a number of reasons, including loss of fluid, an inability to use glucose as a fuel, loss of muscle as protein is broken down and loss of glucose in the urine. Insulin is required as treatment, and is essential for survival. A person with Type 1 diabetes should never stop their insulin even when they are unwell and not eating.
Type 1 diabetes can develop at any age although it is seen more commonly in children and young adults.
The characteristics that indicate Type 1 diabetes are:
rapid development of symptoms of hyperglycaemia (high blood glucose level), that is, frequently passing large amounts of urine, excessive thirst, fatigue and weight loss
development of ketones; if left untreated, ketoacidosis develops.
Question: Can you recall how ketoacidosis develops?
Ketones are produced when the body breaks down fat to use as a fuel. This would normally happen, for example, in a person who did not have diabetes who was fasting. If the level of insulin is not enough to provide sufficient glucose for the tissues to process the ketones, as in diabetes, the level of ketones builds up. This results in increased acid levels in the body – ketoacidosis (Section 3.6).
High blood acid levels are harmful to normal body processes, and if left untreated, can cause vomiting and severe loss of fluid. If treatment is not given quickly the person could die. Fortunately death from ketoacidosis is a very rare event in the western world. If ketoacidosis does occur, therapy in hospital is usually successful, correcting the acid level and returning the blood glucose level to normal.
Many conditions are caused by autoimmunity. The body produces substances called antibodies that usually protect the body from disease. If the body is attacked by an organism that it recognises from a previous infection, the antibodies are ready to destroy the organism. If it is a new organism that the body does not recognise, the body produces a new antibody to get rid of it. This may take a few days and, in the meantime, the person may be unwell with the illness. Occasionally the body produces antibodies which, instead of, or as well as attacking organisms, also attack parts of the body – autoimmunity. In the case of Type 1 diabetes the antibodies destroy the β (beta) cells in the pancreas. Where Type 1 diabetes is due to destruction in this way, we call it an autoimmune disease. Why this happens is unknown, but there is evidence to suggest that genes (hereditary factors) may play a part. A person with Type 1 diabetes may also have other autoimmune diseases such as thyroid disease. Environmental factors, for example certain toxins, may also be important in triggering the development of Type 1 diabetes.
Interestingly, worldwide, the incidence of Type 1 diabetes varies enormously. Incidence describes how many new cases of a disease have happened over a certain period of time (usually a year). There is a tendency to more diabetes in more Northern countries, with Nordic countries, especially Finland, having a particularly high incidence. The reason for this is not understood.
Activity 4, which you should try now, asks you to think about Type 1 diabetes in more detail.
Activity 4: Diagnosing Type 1 diabetes
Read Case study 4, which describes Jennifer's experience. As you read it, think about the features that suggest that Jennifer has diabetes and why it might be Type 1 diabetes.
Case study 4
Jennifer is 30 years old. She is married with one child. She works part time as a teacher. Over the last 4 weeks she has lost 6 kg in weight, dropping from 64 kg to 58 kg and is feeling tired. She has noticed that she is thirsty and has to get up frequently at night to go to the toilet. She does not want to go the doctor because she is worried that she may have diabetes. Her mother had diabetes, which was treated with tablets for 10 years, and she was changed to insulin shortly before she died in hospital with a heart attack. Jennifer very strongly associates her mother's death with starting insulin.
Jennifer's husband Gary notices that she is looking unwell and persuades her to see her GP.
The GP immediately considers the symptoms to indicate diabetes. The GP asks Jennifer to provide a sample of urine. He tests it with a test stick, finding lots of glucose but no ketones. He checks a random blood glucose sample on a glucose meter at the surgery. The level is 28 mmol/l. He sends a sample of whole blood to the laboratory to confirm the reading and asks her to return the next day for a fasting glucose test to confirm the diagnosis.
Jennifer has marked symptoms of hyperglycaemia. She is thirsty and is passing lots of urine, particularly at night. Jennifer has also had very rapid weight loss.
A random glucose test on a meter in the surgery is high and well above the value needed to diagnose diabetes. If you look back to the WHO classification of diabetes in Section 4, only one high glucose level is needed if other symptoms are present. However, the finger-prick blood sample must be confirmed with a laboratory plasma sample. This may be done at the first visit and does not require the patient to return for a fasting test. It is common for people to think that diabetes can only be diagnosed on a blood sample taken first thing in the morning before eating. However, a random blood glucose test result equal to or more than 11.1 mmol/l with symptoms of diabetes is enough to make a diagnosis.
Jennifer did not have ketones in her urine. This does not mean that she does not have Type 1 diabetes, though if they were present it would confirm a diagnosis of Type 1. It depends at what stage the diagnosis is made during the development of Type 1 diabetes as to whether ketones are present. Jennifer's diagnosis has been made early, and ketones have not yet developed. So the speed of the symptoms coming on and the large weight loss would make one think that this patient has Type 1 diabetes. Jennifer will need insulin to control her blood glucose level.