Type 1.5 diabetes: what it is and how it is diagnosed

You are probably familiar with type 1 and type 2 diabetes, but may know less about type 1.5 diabetes.

Type 1.5 diabetes, also called latent autoimmune diabetes in adults (LADA), combines characteristics of both type 1 and type 2 diabetes.

Awareness of the condition recently increased after Lance Bass, known for being part of the iconic American pop group NSYNC, disclosed that he has it.

But what exactly is type 1.5 diabetes, and how is it identified and managed?

Diabetes comes in several forms

Diabetes mellitus describes a group of conditions in which glucose (sugar) levels in the blood are above the normal range. Although there are more than ten forms of diabetes, type 1 and type 2 are the most common.

Type 1 diabetes is an autoimmune condition. The immune system attacks and destroys insulin-producing cells in the pancreas, leaving the body with little or no insulin production.

Insulin is needed to transfer glucose from the bloodstream into cells, where it can be used as energy. This is why people with type 1 diabetes require daily insulin medication. Type 1 diabetes generally develops in children and young adults.

Type 2 diabetes is not autoimmune. Instead, the body's cells gradually become resistant to insulin, while the pancreas can no longer produce sufficient insulin to compensate for that resistance. In contrast to type 1 diabetes, people with type 2 diabetes continue to make some insulin.

Although type 2 is more prevalent among adults, it is increasingly diagnosed in children and young people. Treatment may involve changes to behaviour, including diet and physical activity, alongside oral medicines and insulin therapy.

How type 1.5 diabetes differs from type 1 and type 2

As with type 1 diabetes, type 1.5 diabetes occurs when the immune system attacks pancreatic cells that produce insulin. However, its progression is slower, meaning people with type 1.5 diabetes do not usually need insulin straight away. Most will need insulin within five years of diagnosis, whereas people with type 1 typically require it from the time they are diagnosed.

Type 1.5 diabetes is generally diagnosed in people aged over 30, probably because the condition progresses slowly. This is later than the usual age of onset for type 1 diabetes, but earlier than the typical age at which type 2 diabetes is diagnosed.

It shares genetic and autoimmune risk factors with type 1 diabetes, including particular gene variants. However, evidence also suggests lifestyle factors, such as obesity and physical inactivity - more commonly linked with type 2 diabetes - may play a role.

Symptoms and treatment for type 1.5 diabetes

Symptoms of type 1.5 diabetes vary widely. Some people experience none, while others may have:

• increased thirst
• frequent urination
• fatigue
• blurred vision
• unintentional weight loss.

Initially, type 1.5 diabetes is commonly managed with oral medicines intended to keep blood glucose within the normal range. Depending on glucose control and the medicine being taken, people with type 1.5 diabetes may need to check their blood glucose regularly during the day.

If average blood glucose rises above the normal range despite oral medication, treatment may move on to insulin. However, there are no universally agreed management or treatment approaches for type 1.5 diabetes.

Type 1.5 diabetes is frequently misdiagnosed

Lance Bass said he was first diagnosed with type 2 diabetes before discovering that he actually had type 1.5 diabetes. This is not especially unusual: estimates indicate that type 1.5 diabetes is incorrectly diagnosed as type 2 diabetes 5–10% of the time.

Several factors may explain why.

Firstly, diagnosing type 1.5 diabetes accurately and telling it apart from other forms of diabetes requires specialised antibody testing - a blood test that identifies autoimmune markers. Healthcare professionals do not always request these tests as a matter of routine, either because of cost or because they may not consider them.

Secondly, because type 1.5 diabetes is commonly diagnosed in adults, doctors may incorrectly assume a person has type 2 diabetes, which is more prevalent in this age group. By comparison, type 1 diabetes usually affects children and young adults.

Thirdly, people with type 1.5 diabetes often initially produce enough insulin to control their blood glucose without beginning insulin medication. This can make the condition resemble type 2 diabetes, in which people also make some insulin.

Finally, because its symptoms are similar to those of type 2 diabetes, type 1.5 diabetes may initially be treated as type 2.

We are still learning about type 1.5 diabetes

Far less research has examined how common type 1.5 diabetes is than has investigated type 1 and type 2 diabetes, particularly among non-European populations. In 2023, type 1.5 diabetes was estimated to account for 8.9% of all diabetes cases, a proportion similar to type 1. More research is needed to establish accurate figures.

Limited awareness of type 1.5 diabetes, together with unclear diagnostic criteria, has hindered our understanding of the condition.

A wrong diagnosis can be confusing and stressful. For people with type 1.5 diabetes, being diagnosed with type 2 diabetes may prevent them from receiving the insulin they need promptly. This may worsen their health and increase the likelihood of complications later on.

An accurate diagnosis enables people to access the most suitable treatment, save money and reduce diabetes distress. If you have symptoms that you believe could signal diabetes, or you are uncertain about a diagnosis you have received, keep track of your symptoms and speak to your doctor.

Emily Burch, Accredited Practising Dietitian and Lecturer, Southern Cross University and Lauren Ball, Professor of Community Health and Wellbeing, The University of Queensland

This article is republished from The Conversation under a Creative Commons licence. Read the original article.