How Doctors Tell Type 1 and Type 2 Diabetes Apart: What a Large Study Reveals

Type 1 and Type 2 diabetes are two distinct conditions with very different causes and treatment needs. Type 1 is an autoimmune condition requiring insulin from the outset, while Type 2 typically involves insulin resistance and develops over time. For hospitals, clinics, and health systems to plan services and resources properly, they need to know how many people in their population have each type. But getting accurate numbers isn't always straightforward.

Researchers in Norway decided to test whether standard health registry data—the electronic records that doctors and hospitals already keep—could be used to reliably separate Type 1 from Type 2 diabetes cases.

Scientists examined health records for all adults aged 18 and older living in Norway in 2022—more than 4.3 million people. They created a three-step classification system that looked at information routinely collected in medical records: whether someone used insulin, whether they had received a Type 1 or Type 2 diagnosis from a specialist, and whether they had a diagnosis recorded in primary care.

They then checked how well their method matched diagnoses recorded in the Norwegian Diabetes Register for Adults, which serves as a reference standard for accurate diabetes classification.

The registry-based method performed very well overall. It correctly identified Type 1 diabetes 95.2% of the time and Type 2 diabetes 97.6% of the time. However, accuracy varied by age. For people aged 18 to 59, the method was highly accurate for both types. For those aged 60 to 79, Type 1 identification dropped to 87.6% accuracy. For people over 80, accuracy fell further to 69.4%, likely because older adults may have received their diagnoses long ago when classification practices differed.

When applied to the entire Norwegian population in 2022, the method identified 31,264 adults with Type 1 diabetes (0.72% of the adult population) and 239,120 with Type 2 diabetes (5.5% of the adult population).

This study demonstrates that health systems can rely on data they already collect to get accurate counts of how many people have Type 1 versus Type 2 diabetes. This matters for planning clinics, training specialist providers, and ensuring the right resources—like insulin supplies and diabetes educators—are available where they're needed.

The findings suggest that administrative health registries are a valuable tool for epidemiologists and health officials studying diabetes patterns at the population level, though the method may require extra attention when evaluating very elderly populations.

Source: Scandinavian journal of public health. 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.