Type 1 diabetes mellitus

T1DM

Diabetes mellitus describes a condition which notoriously leads to chronically elevated levels of blood sugar (hyperglycaemia).

Type I DM - autoimmune destruction of insulin-producing β-cells in the pancreas, leading to an absolute deficiency of insulin.

Epidemiology

Type I DM only makes up 10% of DM cases in the UK.

Presentation

It can present at any age, but the highest incidence rate is observed in children aged 10-14 years. In exam land the typical presentation is weight loss, polydipsia, polyuria or a DKA presentation with pear drop smell to the breath. Hyperglycemia causes an osmotic diuresis, leading to polyuria. Which subsequently leads to polydipsia.

Aetiology

• Genetic link: HLA-DR3 and HLA-DR4 +ve individuals are more susceptible.
• Autoimmune association - Addison’s disease, Coeliac disease, Hashimoto’s thyroiditis

Clinical features

• Polyuria
• Polydipsia
• Polyphagia
• Weight loss
• Diabetic ketoacidosis (DKA)* - abdominal pain, hyperventilation, reduced GCS, dehydration
• Poor wound healing
• Recurrent infections - in particular cellulitis and candidiasis
  

*up to 6% of patients with undiagnosed type I DM present with DKA.

Investigations

There are three main investigations used to investigate and diagnose diabetes mellitus:

• Serum glucose - this can be a fasted (no food or drink aside from water for 8-10 hours beforehand) or non-fasted reading.
  ‍
• HbA1c (glycated haemoglobin) - represents the average blood glucose over the past 2-3 months.
  ‍
• OGTT (oral glucose tolerance test) - fasting blood glucose reading is taken, 75g load of glucose is then given and 2 hours after that, blood glucose is measured again.

The following diagnostic criteria for diabetes mellitus has been issued by the World Health Organisation (WHO):

Blood glucose levels:

If the patient is symptomatic:

• Fasting glucose reading ≥7mmol/l
• Random glucose reading ≥11.1mmol/l (or after an OGTT)

If the patient is asymptomatic:

• The above criteria applies, however it will have to be demonstrated on two separate occasions.

HbA1c:

If the patient is symptomatic:

• HbA1c of ≥48mmol/mol (6.5%) is diagnostic of diabetes mellitus in symptomatic patients.

If the patient is asymptomatic:

• Repeat test.

It is recommended that the HbA1c level is repeated within 2 weeks of the original reading.

HbA1c reliability

It is important to note that several conditions may impact HbA1c levels, and thus it may not always be an accurate representation of average blood glucose levels. HbA1c value depends on 2 factors:

• Red blood cell lifespan: reduced = lower HbA1c, increased = higher HbA1c.
  ‍
• Average blood glucose concentration
  

Causes of an underestimated HbA1c:

• Sickle-cell anaemia
  ‍
• G6PD
  ‍
• Hereditary spherocytosis

All of these involve haemolysis of RBCs, thereby reducing their lifespan.

Causes of an overestimated HbA1c:

• Anaemia - RBC lifespan increased to hold onto as much Hb in the body as possible
  ‍
• Splenectomy - RBC lifespan increased because the spleen is not destroying them.
  ‍
• Alcoholism - RBC lifespan increased to compensate for lack of erythropoiesis in the bone marrow, due to excess alcohol intake.

Management

There are three very simple principles underlying the management of diabetes mellitus:

1. Control of blood glucose levels using medication.
   ‍
2. Lifestyle modifications - to increase the chances of achieving glycaemic control, while reducing the risk of developing other health complications related to DM.
   ‍
3. Screening for and managing complications of DM. This will be covered on another learning card.

Lifestyle modifications

Diet -Advise patients to eat a healthy, balanced diet. Patients are usually advised to have three regular meals throughout the day.

Alcohol - advise patients that alcohol may compromise their glycaemic awareness, and that they should avoid having alcohol on an empty stomach as it is absorbed faster. Weekly maximum intake remains the same for diabetics.

Smoking - advise patients to stop smoking to reduce the risk of cardiovascular disease, simultaneously making it less likely for complications related to diabetes to occur.

Exercise - adults are recommended to engage in at least 150 minutes of moderate-intensity exercise a week, spread over at least 3 days, with no more than 2 consecutive days without exercise. In children, this number is down to 60 minutes a week.

Insulin therapy

NICE CKS have issued the following guidance:

“Multiple daily injection basal-bolus insulin regimens are recommended for adults (and children) with type 1 diabetes.”

Basal insulin replacement: twice-daily insulin detemir should be offered, or once-daily insulin glargine if the former is unsuitable.

Bolus insulin replacement: a rapid-acting insulin analogue like NovoRapid should be injected just before meals.

Monitoring

HbA1c

Patients should aim for an HbA1c level of ≤48mmol/mol (6.5%) to minimise the risk of complications.

• HbA1c should be measured every 3-6 months.
  

Blood glucose

NICE CKS advise patients with type I diabetes to:

Monitor blood glucose levels at least 4 times a day, including before meals and bed.

This can increase up to 10 times a day, if the patient...

• Becomes ill
• Exercises (taken before, during and after, ideally)
• Frequency of hypoglycemic episodes increase

Blood glucose targets:

• Fasting plasma glucose levels of 5-7mmol/l on waking.
• Random glucose levels of 4-7mmol/l before meals.
• Adults who test after meals: 5-9mmol/l at least 90 minutes after eating.

“5 to drive, 4 hit the floor”