26th April 2024

A 28-year-old man, previously healthy, presents with a 4-month history of excessive thirst, frequent urination, and significant weight loss of 8 kg despite a good appetite.

A 28-year-old man, previously healthy, presents with a 4-month history of excessive thirst, frequent urination, and significant weight loss of 8 kg despite a good appetite. He has no family history of diabetes. His BMI is 20 kg/m². He reports occasional blurred vision and fatigue. There are no signs of dehydration or acute illness on examination.

Investigations:

Fasting plasma glucose: 14.2 mmol/L (3.9–5.6)

HbA1c: 10.2% (Normal <5.7%)

C-peptide level: 0.5 ng/mL (Normal range 1.1–4.4 ng/mL)

Autoantibodies (including GAD, IA-2): Positive

Serum ketones: Positive

Which is the most likely diagnosis?