Adult-Onset Type 1 Diabetes and LADA: Why Many Cases Go Undiagnosed for Years

When adults develop diabetes, they're usually told they have Type 2 diabetes. But some adults actually have Type 1 diabetes or a related condition called LADA—both autoimmune diseases where the body attacks its own insulin-producing cells. A new study from Siriraj Hospital in Thailand examined how these conditions present differently and why LADA is so often missed.

Researchers reviewed medical records of 84 adults diagnosed with diabetes at age 30 or older between 2014 and 2024. Of these, 32 had typical adult-onset Type 1 diabetes and 52 had LADA. Both groups were followed for years to track how their disease progressed.

The most striking difference between the two conditions is how quickly symptoms appear. Both typical Type 1 diabetes and LADA cause significant weight loss and high blood sugar within roughly one to two months of diagnosis. Both groups had normal body weight at diagnosis, with average BMI around 21.

However, typical Type 1 diabetes often announces itself dramatically. In this study, 77% of patients with typical Type 1 diabetes presented with diabetic ketoacidosis (DKA)—a dangerous condition where the body produces harmful acids and the person becomes severely ill. In contrast, only 3% of LADA patients had DKA at diagnosis. This slower, quieter onset makes LADA easy to confuse with Type 2 diabetes, which develops over months or years.

The study revealed a troubling pattern: nearly 70% of LADA patients were initially diagnosed with Type 2 diabetes. On average, these patients weren't correctly diagnosed until 7.6 years later. During those years, they were likely treated with oral medications designed for Type 2 diabetes, when they actually needed insulin from the start.

The key to avoiding this misdiagnosis is antibody testing. When doctors tested for anti-GAD antibodies—markers of autoimmune attack on insulin-producing cells—all LADA patients tested positive, and 72% of typical Type 1 patients did too. In contrast, Type 2 diabetes patients would test negative for these antibodies. This simple blood test can be the difference between correct and incorrect diagnosis.

By the time of their last follow-up visit, LADA patients showed some important differences compared to those with typical Type 1 diabetes. LADA patients had higher blood pressure, higher HbA1c levels (a measure of long-term blood sugar control), and signs of insulin resistance—the body's reduced ability to use insulin effectively.

LADA patients also experienced more episodes of diabetic ketoacidosis over their disease course, even though they rarely had it at diagnosis. This underscores that LADA, while slower to develop initially, is still a serious autoimmune condition requiring careful management and insulin treatment.

This study highlights the importance of considering autoimmune diabetes in adults, not assuming all adult-onset diabetes is Type 2. Adults who are lean or of normal weight, who experience rapid weight loss, or who don't respond well to Type 2 diabetes medications should be tested for autoimmune markers. A simple anti-GAD antibody test can clarify whether someone has LADA or typical Type 1 diabetes.

Getting the right diagnosis matters because it determines treatment. LADA patients need insulin therapy from the start, even if their symptoms appear mild compared to typical Type 1 diabetes. Early correct diagnosis and proper insulin treatment may help prevent complications and improve long-term outcomes.

Source: Journal of diabetes investigation. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.