A fifth of adults who develop type 1 diabetes over the age of 30 appear to be initially diagnosed with the wrong type, a UK study found.

Work by a team in Exeter found that 20% of adults reported they had type 2 diabetes, despite medical tests later showing they had type 1 diabetes.

While this study was largely based on self-reported diagnoses, it suggests that clinicians may struggle to identify cases of type 1 diabetes in adults.

The work was presented at the European Association for the Study of Diabetes (EASD) 2018 Annual Meeting. A full paper however has not yet been published in a peer-reviewed journal.

Why did they do this study?

Type 1 diabetes can develop at any age over 6 months, but distinguishing between cases of type 1 and type 2 diabetes in adults can be tricky.

As around 90% of cases of diabetes in adults are type 2 however, adults are often assumed to have type 2 when they present with typical diabetes symptoms.

The team from Exeter decided to investigate features of type 1 diabetes in people over 30 and whether people had been correctly diagnosed and given appropriate treatment for type 1 diabetes.

What did they do?

The group enrolled 583 people who were on insulin therapy to manage their diabetes.

The team measured how much C-peptide the participants were producing, which is commonly used as a proxy for how much insulin the body is still able to make naturally. A higher C-peptide measurement is suggestive of type 2 diabetes, while lower C-peptide means type 1 diabetes is more likely.

For comparison, the group also looked at 220 other participants diagnosed with diabetes under the age of 30 who had low enough levels of C-peptide to be indicative of type 1 diabetes.

What did they find?

122 of the 583 adult participants had a severe insulin deficiency according to their C-peptide levels, indicative of type 1. Of these 122 people, 46 (38%) didn’t receive insulin at diagnosis.

In addition, only 79% of these 122 adults reported they had type 1 diabetes, meaning that about 24 people (20%) reported they had type 2. This compares with 100% of the 220 people diagnosed under the age of 30 in the comparison group reporting they had type 1 diabetes.

A researcher from the team stressed that they did not have access to the participants’ medical records at diagnosis however, including their clinicians’ official diabetes diagnosis.

What does this mean for type 1?

These results highlight the difficulty in obtaining a correct diagnosis in adulthood compared with a younger age.

A correct diagnosis however is crucial to ensure people are advised on the most appropriate treatment for their diabetes.

This work suggests that clinicians – and people with diabetes – would benefit from clearer guidelines for diagnosing adults who present with diabetes symptoms.

What’s the next step?

The same team at the University of Exeter told attendees of EASD 2018 about a tool they are currently developing that can help clinicians to predict whether a person is likely to have type 1 or type 2 diabetes, based on a number of different features.