Type 1 diabetes in adults and LADA: when it is not type 2

Most people think type 1 diabetes starts in childhood and type 2 in adults. In reality, a large share of type 1 diabetes begins in adulthood, sometimes in the thirties, forties or later. Because adults are expected to have type 2, they are often given that label first. International experts estimate that a substantial proportion of adults with type 1 diabetes, possibly up to four in ten, are initially misdiagnosed.

What is the difference between type 1 and type 2 diabetes?

In type 1 diabetes, the immune system attacks the beta cells in the pancreas that make insulin. Over time, the body loses its ability to make insulin, so insulin treatment becomes essential.

In type 2 diabetes, the body still makes insulin but does not respond to it well (insulin resistance), and the pancreas gradually cannot keep up. Many people with type 2 do well for years with lifestyle changes and tablets.

What is LADA?

LADA stands for latent autoimmune diabetes in adults. It is an autoimmune diabetes, like type 1, but the immune attack is slower. Typical features are:

• diabetes starting in adulthood, usually after the age of 30
• diabetes antibodies in the blood, most often GAD antibodies
• no need for insulin for at least the first six months after diagnosis

Because the sugar can be controlled with tablets at first, LADA is easily mistaken for type 2. Over months to years, insulin production falls and tablets stop working. Experts still debate whether LADA is a separate type or simply a slower version of type 1. For you, the practical point is the same: your doctor will watch your insulin reserve closely.

What clues suggest type 1 or LADA rather than type 2?

No single feature decides it, but these raise suspicion:

• a normal or low body weight, or weight loss without trying
• sugar that rises quickly or becomes hard to control within a few years, despite good adherence
• ketones in the urine or blood, or an episode of diabetic ketoacidosis (DKA)
• other autoimmune conditions, such as autoimmune thyroid disease, vitiligo or coeliac disease, in you or your family
• few features of insulin resistance, such as a large waist or high triglycerides

Many Indian adults have a mix of features, so tests are usually needed.

Which tests help tell them apart?

• Diabetes antibodies. GAD antibodies are tested first. If negative and suspicion is still high, IA-2 or ZnT8 antibodies may be added. Positive antibodies strongly point to autoimmune diabetes. A negative result does not completely rule it out, because a minority of people with type 1 diabetes have no detectable antibodies.
• C-peptide. This is a marker of how much insulin your own pancreas is making. A low level means your insulin reserve is low. It is best measured with a blood sugar value at the same time, and not right after a very high or very low sugar episode, which can give a misleading result.

Your doctor may repeat C-peptide over time, because in LADA the level tends to fall gradually.

Sometimes a young, lean, antibody-negative person turns out to have a genetic form of diabetes instead. Read MODY: genetic diabetes. In India, diabetes linked to chronic pancreatitis is another possibility. Read about fibrocalculous pancreatic diabetes.

Why does the right diagnosis matter?

Getting the type right changes treatment and safety:

• People with type 1 diabetes or advanced LADA are at risk of DKA, a life-threatening emergency, if they do not get enough insulin.
• In LADA, your doctor will pay attention to which tablets are suitable. Some are less helpful when insulin reserve is low, and some carry a higher risk of DKA in this group.
• Insulin is usually started earlier in LADA once C-peptide is low. Read starting insulin: what to expect.
• People with type 1 diabetes benefit greatly from technology such as CGM sensors and insulin pumps.
• Screening for thyroid and other autoimmune conditions is advised.

What should I do if I think I was misdiagnosed?

Do not stop or change any medicine on your own. Instead, ask your doctor whether antibody and C-peptide tests are appropriate for you, especially if you are lean, your sugar is worsening quickly, or you have other autoimmune conditions. Bring your past reports so your doctor can see how your sugar has changed over time.

What should I ask my doctor?

• Could my diabetes be autoimmune? Should I have GAD antibodies and C-peptide checked?
• Which medicines are safest for my type of diabetes?
• What are the warning signs of ketoacidosis, and how do I check ketones?
• Should I be screened for thyroid or coeliac disease?

If you are unsure of your diabetes type, book a consultation with an endocrinologist.