Differentiating Between Type 1/Type 2 Diabetes, LADA, and MODY

Initial Clinical Assessment

The American Diabetes Association recommends using the AABBCC clinical approach combined with targeted autoantibody and genetic testing to distinguish diabetes subtypes, as misdiagnosis occurs in up to 40% of adults with new-onset diabetes 1, 2
Age of onset <35 years suggests type 1 diabetes or MODY, while onset >35 years suggests type 2 diabetes or LADA 1, 2
Personal or family history of autoimmune disease or polyglandular autoimmune syndromes suggests type 1 diabetes or LADA 1, 2
BMI <25 kg/m² suggests type 1 diabetes, LADA, or MODY, while obesity with metabolic syndrome features suggests type 2 diabetes 1, 2
Strong family history in successive generations (autosomal dominant pattern) suggests MODY 1, 2, 3
Poor glycemic control on non-insulin therapies suggests type 1 diabetes or LADA, while stable mild hyperglycemia suggests MODY 1, 2
Recent immune checkpoint inhibitor therapy can trigger acute autoimmune type 1 diabetes 1, 2

Classic symptoms of polyuria, polydipsia, weight loss, with approximately one-third presenting with DKA in children 4, 5
Can occur at any age, though traditionally associated with younger onset 4, 5
Positive for β-cell autoantibodies (GAD, IA-2, insulin, zinc transporter protein) 6
Absolute insulin deficiency requiring immediate insulin therapy 4, 1

Gradual onset, often asymptomatic, with increased BMI and metabolic syndrome features 6, 1
Typically occurs after middle age, though increasingly seen in younger populations with obesity 4, 5
Negative for β-cell autoantibodies 6
Insulin resistance with progressive β-cell dysfunction on background of insulin resistance 4, 1

Initially appears as type 2 diabetes, but patients progress to insulin dependence within months to years 6
Diagnosed after age 35 years 6
Positive for β-cell autoantibodies (most commonly GAD antibodies) 6

Diabetes diagnosed before age 25 years in non-obese individuals 7, 3
Strong family history across successive generations (autosomal dominant inheritance pattern) 7, 3, 8
Negative for β-cell autoantibodies (though rare coexistence with autoimmune diabetes has been reported) 7, 3
Stable, mild fasting hyperglycemia with A1C between 5.6-7.6% 7, 3
Impaired insulin secretion with minimal or no insulin resistance 7, 3

Test all adults diagnosed with diabetes who are non-obese, <35 years old, or have atypical features for β-cell autoantibodies 6, 9
Consider MODY genetic testing when diabetes is diagnosed in first 6 months of life, before age 25 years with negative autoantibodies, or with a strong family history in successive generations 7, 3, 8

Accurate classification is critical because treatment differs substantially 4, 1
GCK-MODY (MODY2) typically requires no pharmacological treatment except sometimes during pregnancy 7, 3, 8
HNF1A-MODY and HNF4A-MODY are highly sensitive to low-dose sulfonylureas as first-line therapy 7, 3, 8
HNF1B-MODY requires multidisciplinary management for associated renal cysts and organ malformations 3
LADA requires earlier insulin initiation to preserve β-cell function 4, 1
Type 1 diabetes requires immediate insulin therapy 4, 1
Type 2 diabetes initial treatment includes lifestyle modification plus metformin in most cases 8