Differentiating Type 1 From Type 2 Diabetes – The Overview

Following the diagnosis of a child with diabetes mellitus, we must next determine the etiology of their diabetes.

In the past, new-onset diabetes in a child was rarely considered anything other than Type 1 diabetes. However, the incidence of pediatric Type 2 diabetes is rising, and significant overlap in the presentation makes the diagnosis of T1 vs. T2 challenging.

Siller et al. (2020) report the following pitfalls to the current classification of diabetes in children:

1. Depending on age and race/ethnicity, T2DM now accounts for 30-50% of cases in the United States. Elevated BMI, a prior hallmark of T2DM, is now present in 20-40% of children with new-onset T1DM despite the weight loss that often precedes its diagnosis.
2. DKA and markedly elevated HbA1c may also be seen in T2DM at diagnosis. This, in turn, may require immediate initiation of insulin therapy at the time of diagnosis. However, unlike T1DM, sufficient beta-cell function may recover enough to stop insulin therapy and can be further treated with non-insulin agents.
3. Islet autoantibodies may be negative in up to 20% of otherwise classical T1DM, particularly in minority children. Conversely, ~10% of patients with T2DM may have positive autoantibodies (usually GAD or IA-2 antibodies). In these patients, antibody positivity was predictive of later insulin requirements.

Siller et al. also discuss the importance of early and accurate classification of diabetes to mitigate short and long-term complications of diabetes, the psychological impacts, and economic burdens that can result from misclassification.

So how do we distinguish between Type 1 and Type 2 diabetes mellitus?

Figure 1 offers an algorithm that can be used to start thinking about differentiating T1DM from T2DM (if the patient is > six months of age) based on age, obesity, and antibody status.

Table 1 presents other key differences in clinical and laboratory characteristics that can help further determine the final diagnosis of T1DM vs. T2DM.

The remainder of this chapter will explore the differences between Type 1 and 2 diabetes in greater detail regarding epidemiology, pathogenesis, clinical presentations, laboratory findings, and differences in the initial treatment and goals of care.

1. Geffner, M. E., Allen, D. B., & Kappy, M. S. (2014). Pediatric practice: Endocrinology. The McGraw-Hill Companies, Inc.
2. Siller AF, Tosur M, Relan S, Astudillo M, McKay S, Dabelea D, Redondo MJ. Challenges in the diagnosis of diabetes type in pediatrics. Pediatr Diabetes. 2020 Nov;21(7):1064-1073. doi: 10.1111/pedi.13070. Epub 2020 Jul 23. PMID: 32562358.