Hypoglycemia is a group of clinical syndromes in which a decrease in plasma glucose levels, caused by a variety of etiologies, is sufficient to cause corresponding symptoms and signs. To determine whether hypoglycemia needs to be comprehensively judged through qualitative diagnosis, etiological diagnosis, functional experiments, and localization diagnosis. 1. Qualitative diagnosis: When hypoglycemia occurs in diabetic patients, it is diagnosed by carefully inquiring about the history of diabetes and the application of hypoglycemic drugs. Hypoglycemia in non-diabetic patients is diagnosed by the symptoms of hypoglycemia, such as periodic episodes of coma or psychiatric symptoms, blood glucose less than 2.8 mmol/L at the time of the episode, and rapid relief of the symptoms after sugar supply. 2. Etiological diagnosis: through the measurement of plasma or serum insulin, C-peptide, β-hydroxybutyric acid, insulinogen, and combined with functional tests, determine the possible causes of hypoglycemia, such as glucose-lowering drugs, endogenous hyperinsulinemia and so on. 3. Functional tests: such as fasting assessment, 72-hour fasting test, etc. to assist in the diagnosis of etiology. 4. Localized diagnosis: CT, MRI, transabdominal ultrasonography, selective arterial calcium stimulation test, etc. are helpful in localized diagnosis of hypoglycemia. It is recommended to consult a doctor for early diagnosis and treatment under the guidance of a doctor.