Which laboratory pattern most strongly suggests autoimmune beta-cell destruction rather than primary insulin resistance?

• A. Elevated fecal fat content and low serum calcium, which primarily indicate pancreatic exocrine insufficiency rather than beta-cell autoimmunity.
• B. Normal C-peptide with elevated TSH, which confirms hypothyroidism-related hyperglycemia as the primary mechanism instead of autoimmunity.
• C. High C-peptide with markedly elevated fasting insulin, indicating adequate or increased insulin secretion typically seen in primary insulin resistance.
• D. Low or undetectable C-peptide levels with positive islet autoantibodies (e.g., GAD65), indicating poor endogenous insulin production from beta-cell loss.

Answer: (D)