Difficulties of diagnosis: The misclassification of Type 1 Diabetes in older adults

Introduction

Diabetes is a long-term disease characterised by elevated levels of blood sugar (1). There are two main types of diabetes: Type 1 diabetes (T1D) and Type 2 diabetes (T2D). While both types are associated with elevated levels of blood sugar, there are many differences between their causes, the key one being that T1D is autoimmune (where the body’s immune system begins to attack its own healthy cells) (2).

Historically, T1D has been associated with children, young adults, and leaner individuals, compared to T2D patients who are older and more obese (3). However, with obesity increasing in the younger population, an overlap in T1D and T2D characteristics has been reported by recent research, and it has become challenging for clinicians to make the distinction between diabetes types (3,4). This leads to misdiagnosis of patients.

Reasons why misclassification of T1D is more common in older adults

More than 95% of all adult diabetes cases are identified as T2D. This means that an ‘atypical’ clinical presentation of T2D is more likely to occur than a ‘classical’ presentation of T1D. Therefore, as age at diagnosis increases, misclassification of T1D becomes more prevalent (14.2% of those diagnosed above 30 years) (2).

Research into this topic has previously suggested that T1D diagnosed in adulthood presents itself in a milder sense, sharing more similarities with T2D. However, it remains uncertain whether this reported overlap is due to the inclusion of misclassified individuals within datasets.

How misclassification can be reduced through antibody testing

T1D and T2D can be easily differentiated in a lab by testing for autoantibodies, which are only present in T1D due to its autoimmune nature. Therefore, combining a clinician’s diagnosis of T1D with confirmation from an antibody test can provide a much more accurate diagnosis of T1D and significantly reduce misdiagnosis (2,5).

Why is this important?

The treatment of T1D and T2D are very different; T1D requires daily injections of insulin, which is much more invasive than T2D treatment, which can be managed with tablets and lifestyle changes. Correct treatment is imperative for managing patient symptoms and therefore quality of life, due to the chronic nature of diabetes (6).

References 

1.            World Health Organisation. Health Topics: Diabetes [Internet]. Geneva. 2023 [cited 2024 Apr 8]. Available from: https://www.who.int/health-topics/diabetes#tab=tab_1

2.            Krause M, De Vito G. Type 1 and Type 2 Diabetes Mellitus: Commonalities, Differences and the Importance of Exercise and Nutrition. Nutrients. 2023 Oct 7;15(19). doi: 10.3390/nu15194279.

3.            Thomas NJ, Jones AG. The challenges of identifying and studying type 1 diabetes in adults. Vol. 66, Diabetologia. Springer Science and Business Media Deutschland GmbH; 2023. p. 2200–12. Doi: 10.1007/s00125-023-06004-4.

4.            Jones AG, Shields BM, Dennis JM, Hattersley AT, McDonald TJ, Thomas NJ. The challenge of diagnosing type 1 diabetes in older adults. Diabet Med. 2020 Oct;37(10):1781–2. doi: 10.1111/dme.14272.

5.            Thomas NJ, Hill A V, Dayan CM, Oram RA, McDonald TJ, Shields BM, et al. Age of Diagnosis Does Not Alter the Presentation or Progression of Robustly Defined Adult-Onset Type 1 Diabetes. Diabetes Care. 2023 Jun 1;46(6):1156–63. doi: 10.2337/dc22-2159.

6.            Thomas NJ, Jones SE, Weedon MN, Shields BM, Oram RA, Hattersley AT. Frequency and phenotype of type 1 diabetes in the first six decades of life: a cross-sectional, genetically stratified survival analysis from UK Biobank. Lancet Diabetes Endocrinol. 2018 Feb 1;6(2):122–9. doi: 10.1016/S2213-8587(17)30362-5.

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