Type 1 Diabetes

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Overview

Diabetes mellitus is characterised by prolonged hyperglycaemia. Type 1 diabetes mellitus (T1DM) is an autoimmune condition characterised by the destruction of the beta cells in the islets of Langerhans in the pancreas. Since these beta cells produce insulin, their destruction leads to a lack of insulin production, leading to increased blood glucose concentrations.

To help make sense of this chapter, it may be helpful to refer to Endocrine and Metabolic Physiology.

Epidemiology

  • T1DM is most commonly seen in children and young people, but it can still occur and persist into adult life
  • Around 90% of children and young people in the UK who have diabetes have type 1 diabetes

Risk Factors

  • Family history
  • Some environmental factors are thought to play a role (e.g. some viral infections)

Presentation

Features may be quick in onset, over hours to days:

  • Polyuria – excessive thirst
  • Polyuria – excessive passage of urine
  • Weight loss
  • Fatigue – often seen in children/young people

Diabetic ketoacidosis (DKA) is a potentially-life threatening complication of T1DM. See Diabetic Ketoacidosis for more details. Some features suggestive of DKA are:

  • Abdominal pain
  • Vomiting
  • Clinical features of dehydration
  • Tachypnoea
  • Altered consciousness or coma

It is important to note that the incidence of T1DM and DKA is increasing in children and young people. Always suspect them in a young child who is drinking more than usual, having more wet nappies, yet still losing weight. Glucose in the urine of a child should immediately warrant a referral to secondary care for management.

Differential Diagnoses

Type 2 diabetes mellitus

  • Patients are generally older and the onset is slower over weeks – months
  • Acanthosis nigricans may be present – a skin condition suggestive of insulin resistance
  • Weight loss is rare
  • Often picked up incidentally on routine blood tests
  • C-peptide levels are normal/raised
  • Autoantibodies are absent

Maturity onset diabetes of the young (MODY)

  • MODY is due to an autosomal dominant mutation – family history is likely to be present
  • C-peptide levels are normal/raised
  • Autoantibodies are absent

Latent autoimmune diabetes in adults (LADA)

  • The onset is generally after 30 years of age
  • Patients are often misdiagnosed as having type 2 diabetes
  • C-peptide levels are low-normal
  • Some autoantibodies may be present

Investigations

  • Urine dipstick:
    • May show increased glucose
    • Ketonuria may suggest a DKA
  • Fasting blood glucose:
    • ≥7.0 mmol/L – see Diagnosis section on diagnosing T1DM
  • Random blood glucose:
    • ≥11.1 mmol/ L – see Diagnosis section on diagnosing T1DM
    • A helpful way to remember the thresholds for fasting and random blood glucose in diabetes is ‘7-11 fr (For Real)’ for Fasting blood glucose and Random respectively. 
  • HbA1c:
    • ≥48 mmol/mol
    • Not as useful as it reflects hyperglycaemia over the last 3 months and does not show quick fluctuations in blood glucose
  • Coeliac disease screening:
    • All patients with T1DM should be offered screening for coeliac disease due to its association.

Investigations to consider

If the presentation is atypical (e.g. a 50-year-old person presents instead of a child/young adult) consider the following: 

  • C-peptide levels:
    • Low or undetectable
    • Pro-insulin is cleaved to form insulin and C-peptide.
  • Autoantibodies:
    • Glutamic acid decarboxylase antibodies (anti-GAD): may be positive
    • Islet cell antibodies (ICA): may be positive
    • Insulin autoantibodies (IAA): may be positive
    • Insulinoma-associated-2-autoantibodies (IA-2A): may be positive

Diagnosis

World Health Organisation (WHO) criteria

T1DM is diagnosed if:

  • The patient is symptomatic and has one of the following on one occasion:
    • Raised fasting glucose (≥7.0 mmol/L)
    • Raised random glucose (≥11.1 mmol/L)

The patient is asymptomatic but one of the above criteria has been demonstrated on two separate occasions.

Management

Overview

Patients are generally managed by a diabetes specialist plan and are given an individual care plan. Patients are started on insulin regimes by specialists. In general:

  • HbA1c is measured every 3-6 months and should be kept under 48 mmol/mol
  • Blood glucose should be self-monitored at least 4 times a day, including before each meal and before bed
  • Patients should self-monitor more if:
    • They become hypoglycaemic more often
    • During illness
    • During and after sports
    • Planning pregnancy
    • Breastfeeding
    • They have an occupation that requires them to do so (e.g. HGV drivers)
  • Optimal blood glucose targets are:
    • 5-7 mmol/L on waking
    • 4-7 mmol/L before meals at other times of the day

Insulins

Insulins can broadly be categorised based on their time-action profiles:

  • Rapid- and short-acting insulins: quick onset and short duration of action
    • This is to mimic an ‘insulin spike’ that normally occurs in response to glucose absorbed from a meal or sugary drink
  • Intermediate- and long-acting insulins: slow onset and long duration of action
    • This is to mimic the effect of endogenous basal insulin (insulin that is released continuously throughout the day)

Monitoring and Patient Advice

Monitoring

  • Monitor HbA1c every 3-6 months
  • Screen for eye disease annually from 12 years of age
  • Screen for diabetic nephropathy annually from 12 years of age
  • Screen blood pressure annually from 12 years of age

Patient Advice

  • Patients should be referred to a specialist diabetes team to help with dietary choices
  • Due to the increased risk of cardiovascular disease, patients with T1DM should aim to keep a balanced diet low in fat, sugar, and salt
  • Patients should avoid smoking and excess alcohol consumption
  • Patients should be safety-netted on the signs and symptoms of diabetic ketoacidosis

Complications

Microvascular complications

  • Diabetic retinopathy – due to damage to small blood vessels in the kidney
  • Diabetic retinopathy – due to damage to small blood vessels in the retina
  • Diabetic neuropathy – due to direct damage due to hyperglycaemia and decreased blood flow due to damage to small blood vessels supplying the nerves. This includes:
    • Painful diabetic neuropathy
    • Diabetic foot disease
    • Autonomic neuropathy – late-stage complication where there is autonomic nervous system dysfunction. This can lead to reduced hypoglycaemia awareness.
  • Erectile dysfunction
  • Sexual dysfunction in women

Macrovascular complications

Other complications

  • Diabetic ketoacidosis
  • Hypoglycaemia due to insulin treatment
  • Other autoimmune diseases – most commonly thyroid disease, pernicious anaemia and gastritis, coeliac disease, vitiligo, and Addison’s disease
  • Psychiatric complications – e.g. depression and anxiety
  • Infections – particularly skin and urinary tract infections
  • Reduced quality of life
  • Reduced life expectancy – by up to 15 years 

Prognosis

  • Without insulin replacement, a person with T1DM would die within days or weeks
  • With insulin replacement, a person with T1DM can lead a relatively normal life, but at an increased risk of the aforementioned complications.
    • The risk can be reduced by keeping blood glucose concentrations as close to normal as possible.

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