Type 1.5 Diabetes Is a Controversial Diagnosis—Here's What to Know

Diabetes 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. On the other hand, type 2 diabetes most often develops in adults due to insulin resistance, causing high blood sugar levels.

In reality, diabetes is much more complicated. A 2018 study found that over 3% of analyzed cases of diabetes did not fall neatly into either type 1 or type 2. Diabetes can manifest in at least one other form, often called type 1.5. That type of diabetes, explained Ping H. Wang, MD, chair and professor of diabetes, endocrinology, and metabolism at City of Hope Medical Center in Duarte, Calif., has features of both type 1 and type 2.

Here's what to know about the controversial diagnosis—including the symptoms and causes of type 1.5 diabetes, as well as treatments and prevention.

What Is Type 1.5 Diabetes?

Like type 1 diabetes, type 1.5 diabetes has an autoimmune component, which means antibodies from your immune system mistakenly destroy the pancreatic cells which produce insulin. 

Insulin is the hormone needed to get blood sugar out of the bloodstream and into the cells. Without it, glucose accumulates in the blood, leading to potentially life-threatening complications.

However, unlike type 1 diabetes, type 1.5 diabetes does not have to be treated with insulin immediately. It is also generally diagnosed in adults rather than kids.

Those factors make it similar to type 2 diabetes, as does the fact that it progresses much more gradually than type 1 diabetes, explained John B. Buse, MD, PhD, director of the Diabetes Center at the University of North Carolina School of Medicine in Chapel Hill.

"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," explained Deena Adimoolam, MD, weight management specialist at Summit Health in Fair Lawn, N.J. "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."

However, type 1.5 diabetes is not a medical term, and some experts object to its use. The condition is most commonly associated with latent autoimmune diabetes in adults (LADA), and is often used synonymously with that condition.

Causes of Type 1.5 Diabetes

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 regarding the genetic component of type 1.5 diabetes has found that it overlaps with type 1 diabetes and type 2 diabetes. However, 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," explained Dr. Buse. "It's unclear what those are."

Research has discovered 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.

Symptoms of Type 1.5 Diabetes

There are usually no symptoms at the beginning of type 1.5 diabetes. That's because the beta cells are gradually destroyed. So, life tends to continue as usual. Additionally, diabetes complications "generally develop over decades," explained Dr. Buse.

According to Dr. Buse, adults diagnosed with LADA usually develop symptoms when they're 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 glucose levels. According to Dr. Adimoolam, symptoms may include:

• Blurred vision
• Increased urination
• Increased thirst
• Increased hunger
• Increased yeast infections
• Weight loss
• Fatigue

Some people only experience those symptoms after developing diabetic ketoacidosis (DKA). This potentially life-threatening condition happens when stratospherically high blood sugar levels lead to dangerously 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 developing heart disease. People with type 1.5 diabetes may also develop microvascular complications (problems in the small blood vessels)—including neuropathy, retinopathy, and nephropathy.

Diagnosising Type 1.5 Diabetes

Part of diagnosing type 1.5 diabetes or any other form of diabetes is to check for abnormally high blood sugar levels. Still, that test alone won't tell you what type of diabetes you have.

To pinpoint type 1.5 diabetes, healthcare providers will also test for glutamic acid decarboxylase antibodies (GAD), the most common antibodies to destroy insulin-producing 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," explained Dr. Buse. 

"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," added Dr. Buse.

Characteristics suggesting diabetes type 1.5 diabetes include:

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

Another tip-off is that people with LADA typically don't respond well to oral diabetes medications. Still, they do respond well to insulin, said Dr. Buse.

Misdiagnosing Type 1.5 Diabetes

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

For instance, like type 2 diabetes, patients with type 1.5 diabetes typically develop the condition later in life. Additionally, when people with type 1.5 diabetes detect high blood sugar levels, lifestyle changes and medications typically help manage the disease. However, their beta-cell function continues to diminish.

What’s more, type 1.5 diabetes progress more slowly than type 1 diabetes. On the other hand, beta-cell function deteriorates much quicker in type 1.5 diabetes than in type 2 diabetes. Therefore, noninsulin glucose-lowering treatments may initially work in cases of type 1.5 diabetes but become ineffective once beta-cell function drastically declines.

Similarly, C-peptide tests (a standard diagnostic tool for diabetes) will detect low to normal levels in people with type 1.5 diabetes. Similarly, C-peptide levels are negligible in cases of type 1 diabetes. 

But overall, healthcare providers may misdiagnose type 1.5 diabetes due to a lack of awareness surrounding the condition, as well as insufficient means of testing. In some cases, patients with type 1.5 diabetes may try several treatments, including various medications and lifestyle changes, that doesn't effectively help.

Realistically, though, they need insulin therapy or medications to treat their condition to prevent further beta-cell damage.

Research must develop clear diagnostic guidelines to properly diagnose the condition and implement proper treatments early. That way, people with type 1 diabetes can experience positive health outcomes and quality of life. 

Also, efficient ways to test beta-cell function may help healthcare providers easily recognize type 1.5 diabetes. One of the tests for beta-cell function, the average C-peptide plasma concentration (CPAVE), is a lengthy process that requires liquid meals and countless blood samples.

Treating and Preventing Type 1.5 Diabetes

Like everything else about type 1.5 diabetes, treatment has 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.

That may seem strange given that diagnosis usually occurs when patients only have one-tenth the number of original beta cells. 

However, "the pace at which those remaining cells die is much slower [than type 1]," explained Dr. Buse. "So, you can get away with diet modification at the beginning." A carbohydrate-restricted diet often works well, as it does in type 2 diabetes.

Oral medications can also help in those early days, but most will need insulin eventually, added Dr. Adimoolam.

Summary

If you experience symptoms of LADA or type 1.5 diabetes, consult your healthcare provider.

There's no known way to prevent type 1 or 1.5 diabetes. However, you may initially be able to manage type 1.5 diabetes with lifestyle factors like maintaining a healthy weight, sticking to healthy foods, and exercising.