What Is Type 1.5 Diabetes?

Type 1.5 diabetes is a controversial diagnosis that combines features of the main types of diabetes. The health condition is generally categorized into two categories: type 1 and type 2. In type 1 diabetes, antibodies from your immune system destroy the cells that produce insulin. The condition can start suddenly and is usually diagnosed in children. Type 2 diabetes most often develops in adults due to insulin resistance, causing high blood sugar levels.

In reality, diabetes is much more complicated. One study found that over 3% of analyzed cases of diabetes did not fall neatly into either type 1 or type 2 diabetes. Diabetes can manifest in at least one other form, often called type 1.5. This type of diabetes has features of both type 1 and type 2 diabetes.

Like type 1 diabetes, type 1.5 diabetes has an autoimmune component. Antibodies from your immune system mistakenly destroy the pancreatic cells that produce insulin. Insulin is the hormone that helps move blood glucose (sugar) from the bloodstream into cells. Without it, glucose builds up in the blood, which can lead to potentially life-threatening complications.

Type 1.5 diabetes is more similar to type 2 diabetes in several ways. According to John Buse, MD, PhD, director of the Diabetes Center at the University of North Carolina School of Medicine in Chapel Hill, type 1.5 diabetes:

• Does not require immediate insulin treatment
• Is generally diagnosed in adults
• Progresses much more gradually than type 1 diabetes

“It’s a term used to describe patients who have some level of decreased insulin production due to decreased functioning of the beta cells of the pancreas,” Deena Adimoolam, MD, weight management specialist at Summit Health in Fair Lawn, New Jersey, told Health. “Patients with type 1.5 diabetes are able to produce some insulin, but not enough insulin, and over time they may not produce any insulin at all.”

Type 1.5 diabetes is not a medical term, and some experts do not agree with its use. The condition is most commonly associated with latent autoimmune diabetes in adults (LADA), and terms are typically used in similar ways.

No one knows why antibodies that typically guard against foreign invaders decide instead to destroy the body’s insulin-producing cells. Genetics plays a role in all forms of diabetes. Research has found that type 1.5 diabetes overlaps with type 1 and type 2 diabetes. It has more in common with type 1 diabetes than with type 2 diabetes.

Even when genes are involved, an environmental trigger usually sets the process in motion, regardless of the disease. “You have to have the right genetic predisposition, but something has to set your immune system off on a course to destroy the cells that make insulin. It’s unclear what those are,” said Dr. Buse

Research has found links with weight, viral infections, and stress, but nothing is certain. It’s also possible that type 2 diabetes morphs into type 1.5 diabetes. “Some patients with type 2 diabetes who are not well-controlled […] may develop ‘beta cell burnout’ over time where their pancreas produces less insulin,” said Dr. Adimoolam.

There are usually no symptoms at the beginning of type 1.5 diabetes because the beta cells are gradually destroyed. Diabetes complications also “generally develop over decades,” said Dr. Buse.

According to Dr. Buse, adults diagnosed with LADA usually develop symptoms when they are down to about 10% of the typical number of beta cells. Once symptoms appear, they are similar to those for other forms of diabetes and tend to be caused by high blood sugar levels:

• Blurry vision
• Fatigue
• Frequent urination
• Increased hunger and thirst
• Regular yeast infections
• Weight loss

Some people only have these symptoms after developing diabetic ketoacidosis (DKA). This potentially life-threatening condition happens when high blood sugar levels lead to high acid levels in the bloodstream.

Long-term complications of type 1.5 diabetes are similar to type 1 and type 2 diabetes, like an increased risk of heart disease. People with type 1.5 diabetes may also develop microvascular (small blood vessels) complications, such as neuropathy (nerve damage).

Part of diagnosing type 1.5 diabetes or any other form of diabetes is to check for abnormally high blood sugar levels. This test alone will not tell you what type of diabetes you have. Healthcare providers will also test for glutamic acid decarboxylase antibodies (GAD), which are the most common antibodies that destroy pancreatic cells in people with type 1.5 diabetes.

“Antibody tests are positive in about 70% of cases, but there are antibody-negative patients,” said Dr. Buse. When investigating LADA, healthcare providers also look for traits of “atypical diabetes.”

“If everything aligns—if someone has a strong family history of type 2 and they’re overweight, they have high blood pressure and high triglycerides and a lot of features of metabolic syndrome—they likely have type 2,” said Dr. Buse.

Characteristics suggesting diabetes type 1.5 diabetes include:

• Having a family history of autoimmune disorders
• Not being obese
• Weight loss

Another tip-off is that people with LADA typically do not respond well to oral diabetes medications. According to Dr. Buse, they do respond well to insulin.

The differences between LADA or type 1.5 diabetes and other types of diabetes may be subtle. Healthcare providers often mistake the condition for type 2 diabetes. As many as 2-12% of all adult-onset diabetes may be LADA. Many people with type 1.5 diabetes receive the wrong kind of treatment.

Healthcare providers may misdiagnose type 1.5 diabetes due to a lack of awareness and insufficient means of testing. For example: 

• Type 1.5 and type 2 diabetes typically develop later in life, and lifestyle changes and medications typically help manage both types. With type 1.5, beta-cell function continues to decline.
• Type 1.5 diabetes progresses more slowly than type 1 diabetes. Beta-cell function declines much faster in type 1.5 diabetes than in type 2 diabetes. Non-insulin glucose-lowering treatments may initially work for type 1.5 diabetes but become ineffective once beta-cell function drastically declines.
• C-peptide tests (a standard diagnostic tool that tests a person’s ability to make their own insulin) will detect low to normal levels in people with type 1.5 diabetes. C-peptide levels will be low or undetectable in cases of type 1 diabetes.

People with type 1.5 diabetes may try several medications and lifestyle changes that do not effectively manage the condition. They may need insulin therapy or medications that prevent further beta-cell damage.

Clear diagnostic guidelines to diagnose type 1.5 diabetes would help people with type 1 diabetes experience more positive health outcomes and improved quality of life. Efficient ways to test beta-cell function may also help healthcare providers easily recognize type 1.5 diabetes.

Like everything else about type 1.5 diabetes, treatment and prevention have settled on the halfway mark between type 1 and type 2 diabetes. People with type 1.5 will eventually need insulin, but usually not right away.

This may seem strange given that diagnosis usually occurs when people only have 10% the number of original beta cells. However, “the pace at which those remaining cells die is much slower [than type 1],” said Dr. Buse. “You can get away with diet modification at the beginning.”

A carbohydrate-restricted diet often works well, as it does in type 2 diabetes. According to Dr. Adimoolam, oral medications can also help in those early days, but most will need insulin eventually.

Consult a healthcare provider if you have symptoms of LADA or type 1.5 diabetes. There’s no known way to prevent type 1 or 1.5 diabetes. You may initially be able to manage type 1.5 diabetes with lifestyle factors like maintaining your weight, sticking to nutritious foods, and exercising regularly.