Approximately 4 in 10 cases of type 1 diabetes in adults are diagnosed at age 30 years and older, based on data from nearly 1,000 individuals.
New-onset type 1 diabetes in adults is often misdiagnosed as type 2 diabetes, which may lead to inappropriate care, wrote Michael Fang, PhD, of Johns Hopkins University, Baltimore, and colleagues.
Previous research suggests that more than half of type 1 diabetes cases develop in adults, but data on variations in clinical characteristics and age at diagnosis are limited, the researchers said. “Clarifying the burden of adult-onset type 1 diabetes in the general population may help reduce misdiagnosis.”
In a study published in Annals of Internal Medicine, the researchers identified 947 adults aged 18 years and older with newly diagnosed type 1 diabetes, by using data from the National Health Interview Survey between 2016 and 2022. The subjects’ mean age at the time of the survey was 49 years and 48% were women. The racial/ethnic distribution was 73% non-Hispanic White, 10% non-Hispanic Black, 12% Hispanic, 3%, non-Hispanic Asian, and 3% other race/ethnicity.
Overall, 37% of participants were diagnosed with type 1 diabetes after age 30 years, with an overall median age at diagnosis of 24 years.
Type 1 diabetes was diagnosed later in men than in women, at a median age of 27 years vs. 22 years, respectively, and later in racial/ethnic minorities than in non-Hispanic Whites, with a median age of 26-30 years versus 21 years, respectively.
Autoantibody and C-peptide tests are recommended to confirm type 1 diabetes in adults with a suspected diagnosis, but the best method to identify high-risk adults remains unclear, the researchers wrote in their discussion.
“Traditional markers used to differentiate type 1 and type 2 diabetes, such as body mass index, may have limited utility, especially because obesity is now common in the type 1 diabetes population,” they said. New tools combining clinical features and biomarkers may improve accuracy of diagnosis of type 1 diabetes in the adult population, but more research is needed.
The findings were limited by several factors including misclassification based on self-reports of diagnosis and age, the researchers noted. Other limitations included lack of data on diagnostic measures such as levels of autoantibodies, C-peptides, and other indicators of diabetes, as well as inexact subgroup estimates because of small sample sizes.
“We extended existing research by characterizing the age at diagnosis in a nationally representative sample and by documenting variation across race/ethnicity and clinical characteristics,” they said.
The study was supported by grants from the National Heart, Lung, and Blood Institute. The lead authors had no financial conflicts to disclose. Corresponding author Elizabeth Selvin, PhD, disclosed grants from NIH and FNIH, personal fees from Novo Nordisk, other financial relationships with Wolters Kluwer, and nonfinancial support from many pharmaceutical companies outside the current study; she also serves as deputy editor of Diabetes Care and a member of the editorial board of Diabetologia.