What is type 1 diabetes?

When our body detects a microbial infection, it responds by causing inflammation. This helps our immune system fight the infection, and eventually that inflammation will go down once the infection has been resolved.

If our immune system mistakenly attacks healthy cells or tissues, it can be the cause of inflammation and lead to autoimmunity. In T1D, the immune system will mistakenly attack the beta cells in the pancreas. This means T1D is an autoimmune condition.

The antibodies that target the beta cells are called anti-islet autoantibodies, and can be detected in blood tests before any symptoms of diabetes start to appear. The presence of these autoantibodies is often used as a way to predict whether someone is at risk of developing T1D in the future.

As people living with T1D already have an autoimmune condition attacking their beta cells, their immune system is more likely to attack other cells or tissues. That means they’re more likely to also have conditions like coeliac disease and thyroid disease. In fact, it’s estimated that more than 90% of people with T1D and another autoimmune disease also have autoimmune thyroid disease.

Approximately 8.7 million people around the world live with T1D. More than 145,000 of those people live in Australia, and 8 more Australians are diagnosed each day.

People under the age of 30 are most commonly diagnosed with T1D, but it can actually develop at any age. In fact, around half of all people diagnosed with it in Australia are adults.

Taking a closer look at the prevalence of T1D in Australia, the National (insulin-treated) Diabetes Register (NDR) found:

• a similar amount of males and females are living with T1D
• the occurrence of T1D in children and young adults varies depending on their socioeconomic status; the rates were found to be 1.2 times higher among those living in the most disadvantaged areas compared to the least disadvantaged areas.

Many people with T1D start their diabetes diagnosis journey when they visit their GP after noticing something isn’t quite right.

They may be experiencing some of the common symptoms of T1D, including excessive thirst, frequent urination, tiredness and weight loss. People who have had their T1D go unnoticed and untreated for longer could be experiencing a serious condition called diabetic ketoacidosis (DKA), which requires urgent treatment.

GPs and other healthcare providers can carry out several tests for a T1D diagnosis. The first check is often a random blood glucose test, done via a finger prick.

Other tests to diagnose type 1 diabetes include the options below.

Random blood glucose test

The quickest and often the first option for testing for T1D is a random glucose test measuring a patient’s current blood sugar.

A result above 11.1mmol/L indicates diabetes.

Fasting blood glucose test

This is a blood test typically conducted in the morning after fasting overnight. The fasting helps give doctors a clear look at how the body manages blood glucose levels without the impact of food intake.

For this test, any result above 7.0 mmol/L indicates diabetes.

Oral glucose tolerance test

After fasting and an initial blood test, people drink a sugary drink then have their blood glucose tested over the course of approximately two hours. This shows the benchmark glucose level without outside influences and later measures how the body responds to carbohydrate (sugar) intake.

After two hours, if the resulting blood glucose level is 7.8 mmol/L or lower, the person is considered to not have T1D. A result between 7.8 and 11 mmol/L can indicate prediabetes. If it’s 11.1 mmol/L or higher, it’s likely that the person has diabetes.

Glycated haemoglobin (HbA1c) test

The most comprehensive test is the haemoglobin A1c test. This blood test shows the average blood glucose level for about the past 3 months.

Learn more about HbA1c and how it’s tested.

C-peptide

This test measures how much C-peptide is in a person’s blood. C-peptide is a substance that’s made when insulin is produced in the body. When insulin is produced, it is initially created in a form known as proinsulin, which consists of two parts: insulin and C-peptide. The C-peptide is released in a similar pattern as insulin into the bloodstream.

By measuring the levels of C-peptide in someone’s blood, we can get an idea of how much insulin their body is making. Low levels of C-peptide and insulin can suggest a deficiency in insulin production, which is often seen in people with T1D.

By measuring C-peptide levels, doctors can also tell the difference between type 1 and type 2 diabetes.

Autoantibody tests look for autoantibodies in the blood, and they can detect these autoantibodies even before T1D symptoms appear. By screening for autoantibodies, we can identify people who are at risk of developing T1D and intervene early to try to prevent or delay the onset of the condition.

Autoantibody tests can also help distinguish between type 1 and type 2 diabetes. Unlike other T1D diagnosis tests, autoantibody tests can identify people who have latent autoimmune diabetes in adults (LADA), which is sometimes misdiagnosed as type 2 diabetes.

People will often have many autoantibodies tested and measured to confirm a diagnosis of T1D.

Insulinoma-associated-2 autoantibodies (IA-2A)

This test looks for antibodies mounted against a specific enzyme in beta cells. Both the IA-2A and GADA tests (see below) are common T1D autoantibody tests.

The IA-2A test can:

• help distinguish between type 1 and type 2 diabetes
• identify people who are at risk of developing T1D, including those who have family members with the condition
• predict whether someone with adult-onset diabetes will need insulin treatment in the future.

Glutamic acid decarboxylase autoantibodies (GADA or anti-GAD)

This test looks for antibodies built against glutamic acid decarboxylase, a specific enzyme in the insulin-producing pancreatic beta cells. GAD antibodies are present in about 75% of people with T1D at diagnosis.

The GADA test can be helpful in determining which type of diabetes someone has. It can:

• be used to check whether gestational diabetes might be T1D
• measure the progression of T1D
• assesses the risk of developing T1D or LADA.

Zinc transporter 8 (ZnT8Ab)

This test investigates autoantibodies targeting an enzyme specific to beta cells. ZnT8A are some of the newest and least understood islet autoantibodies.

They can indicate the same things as the IA-2A test, but can also predict the future development of diabetes in women experiencing gestational diabetes.

Islet cell cytoplasmic autoantibodies (ICA)

This test identifies a type of islet cell antibodies that are present in up to 80% of people with T1D. While these autoantibodies are very specific to a T1D, the test lacks sensitivity and is rarely used by clinical labs during diagnosis.

There are about 422 million people living with diabetes internationally. T1D accounts for around 10% of all cases, with the remaining 90% living with type 2 diabetes, LADA or gestational diabetes.

Type 2 diabetes

People with type 2 diabetes develop insulin resistance, meaning their body doesn’t use insulin as well as it should. In later stages of type 2 diabetes, people may also not produce enough insulin.

Type 2 diabetes is caused by a combination of genetics and lifestyle factors, such as being overweight or having a sedentary lifestyle. It can often be managed by diet changes, exercise and medication. However, it is a progressive condition, and some people may need to inject insulin in the later stages of the condition.

LADA

Some people who were initially diagnosed as having type 2 diabetes actually have latent autoimmune diabetes of adults (LADA). This is sometimes referred to as type 1.5 diabetes.

People with LADA have features of both type 1 and type 2 diabetes in that their immune system attacks the cells of the pancreas that produce insulin, but they may also have insulin resistance. The destruction of the insulin producing cells is much slower in LADA than in T1D.

For some people, LADA can be managed with diet, exercise and medication. However, most people with LADA will require insulin therapy within the first year after diagnosis.

Gestational diabetes

Gestational diabetes refers to diabetes that is first detected during pregnancy. Pregnant women produce large amounts of hormones such as oestrogen and progesterone, which can cause the body to become resistant to the effects of insulin.

By the time a woman reaches the end of the third trimester, her insulin requirements have tripled. If the pancreas is unable to match this increased demand, blood glucose levels start to rise. In general, blood glucose returns to normal after pregnancy. However, women diagnosed with this type of diabetes are at significantly higher risk of developing type 2 diabetes later in life.