What is type 1.5 diabetes? It’s a bit like type 1 and a bit like type 2 – but it’s often misdiagnosed

Source: The Conversation (Au and NZ) – By Emily Burch, Accredited Practising Dietitian and Lecturer, Southern Cross University

While you’re likely familiar with type 1 and type 2 diabetes, you’ve probably heard less about type 1.5 diabetes.

Also known as latent autoimmune diabetes in adults (LADA), type 1.5 diabetes has features of both type 1 and type 2 diabetes.

More people became aware of this condition after Lance Bass, best known for his role in the iconic American pop band NSYNC, recently revealed he has it.

So, what is type 1.5 diabetes? And how is it diagnosed and treated?

There are several types of diabetes

Diabetes mellitus is a group of conditions that arise when the levels of glucose (sugar) in our blood are higher than normal. There are actually more than ten types of diabetes, but the most common are type 1 and type 2.

Type 1 diabetes is an autoimmune condition where the body’s immune system attacks and destroys the cells in the pancreas that make the hormone insulin. This leads to very little or no insulin production.

Insulin is important for moving glucose from the blood into our cells to be used for energy, which is why people with type 1 diabetes need insulin medication daily. Type 1 diabetes usually appears in children or young adults.

Type 2 diabetes is not an autoimmune condition. Rather, it happens when the body’s cells become resistant to insulin over time, and the pancreas is no longer able to make enough insulin to overcome this resistance. Unlike type 1 diabetes, people with type 2 diabetes still produce some insulin.

Type 2 is more common in adults but is increasingly seen in children and young people. Management can include behavioural changes such as nutrition and physical activity, as well as oral medications and insulin therapy.

How does type 1.5 diabetes differ from types 1 and 2?

Like type 1 diabetes, type 1.5 occurs when the immune system attacks the pancreas cells that make insulin. But people with type 1.5 often don’t need insulin immediately because their condition develops more slowly. Most people with type 1.5 diabetes will need to use insulin within five years of diagnosis, while those with type 1 typically require it from diagnosis.

Type 1.5 diabetes is usually diagnosed in people over 30, likely due to the slow progressing nature of the condition. This is older than the typical age for type 1 diabetes but younger than the usual diagnosis age for type 2.

Type 1.5 diabetes shares genetic and autoimmune risk factors with type 1 diabetes such as specific gene variants. However, evidence has also shown it may be influenced by lifestyle factors such as obesity and physical inactivity which are more commonly associated with type 2 diabetes.

What are the symptoms, and how is it treated?

The symptoms of type 1.5 diabetes are highly variable between people. Some have no symptoms at all. But generally, people may experience the following symptoms:

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

Typically, type 1.5 diabetes is initially treated with oral medications to keep blood glucose levels in normal range. Depending on their glucose control and the medication they are using, people with type 1.5 diabetes may need to monitor their blood glucose levels regularly throughout the day.

When average blood glucose levels increase beyond normal range even with oral medications, treatment may progress to insulin. However, there are no universally accepted management or treatment strategies for type 1.5 diabetes.

Type 1.5 diabetes is often misdiagnosed

Lance Bass said he was initially diagnosed with type 2 diabetes, but later learned he actually has type 1.5 diabetes. This is not entirely uncommon. Estimates suggest type 1.5 diabetes is misdiagnosed as type 2 diabetes 5–10% of the time.

There are a few possible reasons for this.

First, accurately diagnosing type 1.5 diabetes, and distinguishing it from other types of diabetes, requires special antibody tests (a type of blood test) to detect autoimmune markers. Not all health-care professionals necessarily order these tests routinely, either due to cost concerns or because they may not consider them.

Second, type 1.5 diabetes is commonly found in adults, so doctors might wrongly assume a person has developed type 2 diabetes, which is more common in this age group (whereas type 1 diabetes usually affects children and young adults).

Third, people with type 1.5 diabetes often initially make enough insulin in the body to manage their blood glucose levels without needing to start insulin medication. This can make their condition appear like type 2 diabetes, where people also produce some insulin.

Finally, because type 1.5 diabetes has symptoms that are similar to type 2 diabetes, it may initially be treated as type 2.

We’re still learning about type 1.5

Compared with type 1 and type 2 diabetes, there has been much less research on how common type 1.5 diabetes is, especially in non-European populations. In 2023, it was estimated type 1.5 diabetes represented 8.9% of all diabetes cases, which is similar to type 1. However, we need more research to get accurate numbers.

Overall, there has been a limited awareness of type 1.5 diabetes and unclear diagnostic criteria which have slowed down our understanding of this condition.

A misdiagnosis can be stressful and confusing. For people with type 1.5 diabetes, being misdiagnosed with type 2 diabetes might mean they don’t get the insulin they need in a timely manner. This can lead to worsening health and a greater likelihood of complications down the road.

Getting the right diagnosis helps people receive the most appropriate treatment, save money, and reduce diabetes distress. If you’re experiencing symptoms you think may indicate diabetes, or feel unsure about a diagnosis you’ve already received, monitor your symptoms and chat with your doctor.

Emily Burch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Lauren Ball works for The University of Queensland and receives funding from the National Health and Medical Research Council, Queensland Health and Mater Misericordia. She is a Director of Dietitians Australia, a Director of the Darling Downs and West Moreton Primary Health Network and an Associate Member of the Australian Academy of Health and Medical Sciences.

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