The latest diagnostic criteria for diabetes mellitus are the typical symptoms of “three more and one less” (drinking, urinating, eating, and weight loss) plus venous plasma glucose ≥11.1 mmol/L, fasting blood glucose ≥7.0 mmol/L, or 2-hour glucose ≥11.1 mmol/L after a glucose tolerance test at any time of the day. A diagnosis of diabetes is made when one of these three is met. Diabetes mellitus is a group of metabolic diseases characterized by chronic hyperglycemia due to multiple etiologies and caused by defects in insulin secretion and/or utilization. Diabetes mellitus is a clinical syndrome caused by a complex etiology of genetic and environmental factors, but its etiology and pathogenesis are still not fully elucidated. When diabetes is suspected, it is recommended to consult a medical professional for a definitive diagnosis and to follow the doctor’s instructions for treatment.