Overview

• Diabetes produces a variety of clinical presentations, from acute to gradual onset

• Currently, the diagnosis should be based on two separate tests unless the patient is clearly symptomatic in which case only one positive test is required

• New World Health Organization diagnostic criteria based on glycosylated haemoglobin are expected in the near future

• A combination of genetic and environmental factors contribute to the risk of diabetes

• Impaired glucose regulation is an important risk factor both for future diabetes and cardiovascular disease

• Distinction between random and fasting samples is essential in interpreting the significance of borderline blood glucose levels

• Impaired glucose tolerance can only be diagnosed by oral glucose tolerance test

Introduction

Diabetes mellitus is a common metabolic disorder that is defined by chronic hyperglycaemia. Besides symptoms related to hypergly-caemia itself such as thirst, polyuria and weight loss, it may also cause potentially life-threatening acute hyperglycaemic emergencies. It is a major cause of morbidity and premature mortality from long-term complications such as cardiovascular disease, blindness, renal failure, amputations and stroke. With good control of hyperglycaemia established early on and continued life-long, an individual with diabetes can enjoy a good quality of life and reduce the risk of these long-term complications that are so detrimental to their life and wellbeing.

Prevalence of diabetes

In the United Kingdom we have an estimated 1.8 million people with diabetes. However, based on screening studies it is believed that up to a million more maybe undiagnosed (see pages 15 and 17).

The prevalences of both type 1 and type 2 diabetes are increasing. Type 2 diabetes is increasing far more rapidly, driven by increasing life expectancy and the epidemic of obesity. It is believed that there will be as many as 300 million people with diabetes worldwide by the year 2025. Most of this increase will occur in developing countries. The majority of children have insulin-requiring type 1 diabetes, whilst the vast majority of those aged >25 years will have type 2 diabetes (Figure 1.1).

Types of diabetes

The types of diabetes have been classified by the WHO. Type 1 diabetes (previously referred to as insulin-dependent diabetes mellitus or IDDM) is due to absolute insulin deficiency and is usually an autoimmune disease leading to the destruction of the insulin-secreting beta cells in the pancreas. In some cases the cause of destruction of the beta cells is not known.

Type 2 (previously known as non-insulin dependent diabetes mellitus or NIDDM) results from relative insulin deficiency that may be associated with varying degrees of insulin action defects known collectively as insulin resistance.

For a practising clinician the implication of this diagnosis is that patients with type 1 diabetes require insulin straight away and insulin should not be stopped as it is life-preserving. Type 2 patients can progress through several stages and may require insulin later on in their disease.

Risk factors for diabetes

Genetics. Genetic susceptibility is important for both types of diabetes. Family history of type 1 diabetes or other autoimmune diseases such as autoimmune thyroid disease is associated with a higher risk of developing type 1 diabetes in the family. Inheritance in type 2 diabetes is far more complex as there are many underlying causes. Furthermore, the risk varies according to the particular sub-type of type 2 diabetes. A family history of type 2 diabetes in a first degree relative is a strong risk factor for diabetes in that individual.

Obesity. Apart from family history, obesity is a very important risk factor for diabetes. For a given degree of obesity, central or 'apple-shaped' obesity is associated with a much higher risk of

Projected prevalence of diabetes in 2025

Projected prevalence of diabetes in 2025

□ No data available

Total cases = 300 million adults

□ No data available

Total cases = 300 million adults

Figure 1.1 Projected prevalence of diabetes in 2025. Reproduced with permission from the World Health Organisation. The World Health Report. Life in the 21st Century: a vision for all. Geneva: WHO, 1998.

progression to type 2 diabetes than those who have lower body obesity or are 'pear-shaped'. Those with a body mass index (BMI) of >25k/m2 or high waist circumference (Table 1.1) are at a higher risk of developing diabetes and should be encouraged to take regular exercise and eat healthily (Figure 1.2).

Age. Beta cell function declines with age, indeed if we live long enough all of us have the potential to develop diabetes at some stage. With an aging population an increase in prevalence of diabetes can be expected.

Ethnicity. People of South Asian or Afro-Caribbean origin are at higher risk of developing diabetes. They are also more likely to have type 2 diabetes presenting at a young age and usually have poorer risk factor control. South Asian patients have a high risk of developing diabetic renal disease and also coronary artery disease. Afro-Caribbean patients are more likely to have strokes and have a higher risk of gestational diabetes. South Asian and Hispanic children may develop type 2 diabetes.

Initial presentation and diagnosis

The commonest presentation is tiredness, thirst, polyuria, weight loss, pruritus vulvae or balanitis. It is not uncommon for this

Table 1.1 The International Classification of adult underweight, overweight and obesity according to BMI (adapted from WHO guidelines, http://apps. who. int/bmi/index. jsp?introPage=intro_3. html)

BMI(kg/m2)

Table 1.1 The International Classification of adult underweight, overweight and obesity according to BMI (adapted from WHO guidelines, http://apps. who. int/bmi/index. jsp?introPage=intro_3. html)

BMI(kg/m2)

Classification

Principal cut-off points

Additional cut-off points

Underweight

<18.50

<18.50

Normal range

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