A 45-year-old male patient presents with persistent hyperglycemia (fasting blood glucose

A 45-year-old male patient presents with persistent hyperglycemia (fasting blood glucose

A 45-year-old male patient presents with persistent hyperglycemia (fasting blood glucose: 12.3 mmol/L) and polyuria. Laboratory tests show decreased serum insulin levels. Which type of diabetes mellitus is most likely?

A. Type 1 diabetes mellitus

B. Type 2 diabetes mellitus

C. Gestational diabetes mellitus

D. Secondary diabetes mellitus

Answer: A

Explanation: Type 1 diabetes mellitus is characterized by autoimmune destruction of pancreatic β-cells, leading to absolute insulin deficiency (decreased serum insulin). It often occurs in younger patients, but can develop in adults. Type 2 diabetes is associated with insulin resistance and relative insulin deficiency (B is incorrect). Gestational diabetes occurs during pregnancy (C is incorrect), and secondary diabetes is caused by other diseases (e.g., chronic pancreatitis, D is incorrect).