Type 1 diabetes mellitus

• Approximately 15% of those with diabetes - usually juvenile-onset, but may occur at any age. It may be associated with other autoimmune diseases. It is characterised by insulin deficiency.
• Concordance is >30% in identical twins; four genes are thought to be important. One (6q) determines islet sensitivity to damage - eg, from viruses or cross-reactivity from cow's milk-induced antibodies.
• Associated with HLA DR3 and DR4 and islet cell antibodies around the time of diagnosis. Patients always need insulin treatment and are prone to ketoacidosis.
• Risks of developing type 1 diabetes are broadly similar in all ethnic groups; however, there is increasing evidence that certain infectious agents or certain components of diet in early childhood trigger the development of autoimmunity to the pancreatic beta cells in genetically susceptible individuals.
• The term 'type 1a diabetes' is applied to the development of type 1 diabetes resulting from an autoimmune T cell-mediated islet cell destruction.^[3] 

Type 2 diabetes mellitus

• Approximately 85% of those with diabetes; they are usually older at presentation (usually >30 years of age) but it is increasingly diagnosed in children and adolescents.^[4] 
• Type 2 diabetes is associated with excess body weight and physical inactivity.
• All racial groups are affected but increased prevalence in people of South Asian, African, African-Caribbean, Polynesian, Middle-Eastern and American-Indian ancestry.
• Caused by impaired insulin secretion and insulin resistance and has a gradual onset.
• Type 2 diabetics may eventually need insulin treatment.

Prevalence^[5] 

• In 2011 there were 2.9 million people with diabetes. It is estimated that five million people will have diabetes in the UK by 2025.
• It is estimated that there are around 850,000 people in the UK who have diabetes but have not been diagnosed.
• The UK average prevalence of diabetes in the UK is 4.45% but there are variations between countries and regions.
• The proportion of people with diabetes increases with age.
• However, the incidence of diabetes is increasing in all age groups. Type 1 diabetes is increasing in children (especially those aged <5 years), and type 2 diabetes is increasing, particularly in black and minority ethnic groups.

Risk factors for type 2 diabetes^[6] 

• Obesity, especially central (truncal) obesity.
• Lack of physical activity.
• Ethnicity: people of South Asian, African, African-Caribbean, Polynesian, Middle-Eastern and American-Indian descent are at greater risk of type 2 diabetes, compared with the white population.
• History of gestational diabetes.
• Impaired glucose tolerance.
• Impaired fasting glucose.
• Drug therapy, eg combined use of a thiazide diuretic with a beta-blocker.
• Low-fibre, high-glycaemic index diet.
• Metabolic syndrome.
• Polycystic ovarian syndrome.
• Family history (2.4-fold increased risk for type 2 diabetes).
• Adults who had low birth weight for gestational age.

Presentation

• Patients with all types of diabetes may present with polyuria, polydipsia, lethargy, boils, pruritus vulvae or with frequent, recurrent or prolonged infections.
• Patients with type 1 diabetes may also present with weight loss, dehydration, ketonuria and hyperventilation. Presentation of type 1 diabetes tends to be acute with a short duration of symptoms.
• Presentation in patients with type 2 diabetes tends to be subacute with a longer duration of symptoms.
• Patients with diabetes may present with acute or chronic complications, as outlined in the section 'Complications', below.

Diagnosis

• Diabetes may be diagnosed on the basis of one abnormal plasma glucose (random ≥11.1 mmol/L or fasting ≥7 mmol/L) in the presence of diabetic symptoms such as: thirst, increased urination, recurrent infections, weight loss, drowsiness and coma.
• In asymptomatic people with an abnormal random plasma glucose, two fasting venous plasma glucose samples in the abnormal range (≥7 mmol/L) are recommended for diagnosis.
• Two-hour venous plasma glucose concentration ≥11.1 mmol/L two hours after 75 g anhydrous glucose in an oral glucose tolerance test (OGTT).
• The World Health Organization (WHO) now recommends that glycated haemoglobin (HbA1c) can be used as a diagnostic test for diabetes. An HbA1c of 48 mmol/mol (6.5%) is recommended as the cut-off point for diagnosing diabetes. A value less than 48 mmol/mol does not exclude diabetes diagnosed using glucose tests.^[7] 

Assessment and monitoring

• Assessment: see separate article Assessment of the Established Diabetic.
• Monitoring: see separate articles Glycated Haemoglobin and Self-Monitoring in Diabetes Mellitus.

Management

The management plan for a person with diabetes includes:^[6] 

• Diabetes education: structured education and self-management (at diagnosis and regularly reviewed and reinforced) to promote awareness.
• Diet and lifestyle: healthy diet, weight loss if the person is overweight, smoking cessation, regular physical exercise.
• Maximising glucose control while minimising adverse effects of treatment, such as hypoglycaemia.       
• Reduction of other risk factors for complications of diabetes, including the early detection and management of hypertension, drug treatment to modify lipid levels and consideration of antiplatelet therapy with aspirin.
• Monitoring and early intervention for complications of diabetes, including cardiovascular disease, feet problems, eye problems, kidney problems and neuropathy.

A global assessment of an individual's cardiovascular risk is essential.

See separate articles:

• Management of Type 1 Diabetes.
• Management of Type 2 Diabetes.
• The Newly Diagnosed Diabetic.
• Diabetes Diet and Exercise.
• Diabetes Education and Self-management Programmes.
• Antihyperglycaemic Agents used for Type 2 Diabetes.
• Insulin Regimens.
• Precautions with Diabetic Patients Undergoing Surgery.
• Diabetes and Intercurrent Illness.
• Diabetes in Pregnancy.

Complications

Refer to separate articles under 'Acute' and 'Chronic' headings in this section.

Acute

• See Diabetic Ketoacidosis and Hyperosmolar Hyperglycaemic State.
• See Emergency Management of Hypoglycaemia.

Chronic

• Cardiovascular disease: see ischaemic heart disease (Stable Angina, Acute Coronary Syndrome), Cerebrovascular Events and Peripheral Arterial Disease.
• See Diabetic Nephropathy.
• See Diabetic Retinopathy and Diabetic Eye Problems.
• See Diabetic Neuropathy, Autonomic Neuropathy and Neuropathic Pain and its Management.
• See Diabetic Foot, Leg Ulcers and Painful Foot.
• Frequent, recurrent and persistent infections.

Prognosis

• Type 1 diabetes:^[8]
  • Over 60% of patients with type 1 diabetes have reasonably good health but many of the remainder develop blindness, end-stage renal disease and, in some cases, early death.
  • If a person with type 1 diabetes survives the period 10-20 years after onset of disease without ongoing complications, they have a good chance of reasonably good health.
  • Controlling blood glucose, lipids, blood pressure and weight are important prognostic factors.
• Type 2 diabetes:^[6]
  
  • 75% of people with type 2 diabetes will die of heart disease and 15% of stroke.
  • The mortality rate from cardiovascular disease is up to five times higher in people with diabetes than in people without diabetes.
  • For every 1% increase in HbA1c level, the risk of death from a diabetes-related cause increases by 21%.

Prevention

Type 1: despite a great deal of ongoing research, there are currently no interventions before diagnosis that have shown any benefit.^[9] 

Type 2: see separate article Prevention of Type 2 Diabetes.