With the popularity of glucose meters, many people accidentally test themselves with high blood sugar and wonder if they have diabetes. If you accidentally test high blood sugar, you usually have to go to the hospital for an oral glucose tolerance test (OGTT) to confirm the diagnosis. The blood glucose we measure to diagnose diabetes refers to venous plasma blood glucose, not capillary blood glucose which we test with a blood glucose meter. The oral glucose tolerance test (OGTT) is the primary method for diagnosing DM, hypoglycemia (IGF). After a normal person consumes a large amount of glucose at one time (the international standard dose is 75g of anhydrous glucose), the blood glucose concentration increases slightly and returns to normal within 2h. This phenomenon is called glucose tolerance phenomenon. If endocrine disorders (such as stress and certain endocrine diseases) or nervous system dysfunction cause abnormal glucose metabolism, the blood glucose concentration may rise sharply after consuming a large amount of glucose, and cannot return to normal level within 2h, which is called hypoglycemic tolerance or diabetes mellitus. OGTT should be performed under fasting condition, and fasting should not be less than 10h, nor more than 16h, but water can be consumed. The test should be performed from 7 to 9 am. During the test, the subject should pay attention to rest as much as possible, strictly prohibit strenuous physical activity, and avoid mental stimulation and other stressful stimuli. Blood should be collected for 5 times after fasting (0 min) and 30, 60, 120 and 180 min after taking sugar. If the patient has a history of hypoglycemia, the test time should be extended and blood should be taken for blood glucose measurement in the 4th and 5th hours. During the test, if there is pallor, nausea and fainting, the test should be stopped, and the test can be replaced by oral administration of 100g of standard flour buns instead of glucose. The current global criteria for diabetes mellitus: 1, fasting blood glucose ≥ 7.0 mmol/L. Fasting status is defined as no caloric intake for at least 8h. 2, DM symptoms, and casual blood glucose ≥ 11.1 mmol/L. Casual blood glucose refers to the blood glucose value at any time after the meal, and the typical DM symptoms are polyuria, polydipsia, polyphagia and wasting. 3, OGTT 2h plasma glucose (PG) ≥ 11.1 mmol/L. OGTT is still performed according to WHO requirements. Patients who meet one of the above criteria and still meet one of the three criteria at the next day follow-up are diagnosed as DM. FPG ≥ 6.1 mmol/L (110 mg/dl) but < 7.0 mmol (126 mg/dl) is defined as abnormal fasting glucose, and FPG < 6.1 mmol/L as normal fasting glucose (NFG). Does OGTT meeting the above criteria necessarily diagnose diabetes? No, we also need to exclude the existence of the following diseases or states: (i) Dietary factors Sufficient caloric carbohydrate should be consumed three days before the test, generally it should be greater than 250g/day, especially for elderly patients, otherwise, eating too little before will lead to excessive absorption and false blood glucose elevation on the day of the test. (B) Physical activity Strenuous physical activity before taking sugar can also cause blood sugar to rise significantly. (3) Mental factors Emotional excitement can raise blood glucose and cause persistent hyperglycemia, so care should be taken to avoid mental stimulation during the test. (iv) Physiological factors The abnormal intestinal absorption function of the subject should be changed to intravenous glucose tolerance test. （Oral contraceptives, niacin and certain diuretics can reduce glucose tolerance. Contraceptives should be discontinued one week before the test, and the latter two should be discontinued 3 to 4 days before the test. Oral hypoglycemic agents, sodium salicylate, or propranolol (Takayasu) should be discontinued 3 days prior to the trial. Those who use monoamine oxidase inhibitors should stop taking them for more than one month. Other drugs that affect the OGTT results are lipid-lowering drugs, emulsified fat solution, drinking large amounts of coffee, etc. (F) stress Various physiological stress (excessive excitement, excessive physical activity) and various pathological stress (such as fever, infection, hemorrhage, trauma, surgery, anesthesia, coma, etc.) have a significant impact on the OGTT, the common feature is that due to the increase in stress hormones, glucose tolerance decreases, showing a diabetic-like response, therefore, the OGTT test can not be done during stress. (vii) diseases There are many pathological conditions and diseases that affect OGTT changes. 1, liver disease When the liver function is reduced, hyperglycemic or hypoglycemic response can occur, and the OGTT of patients with liver disease is mostly abnormal. 2, Heart disease The development of coronary heart disease is closely related to insulin resistance, which occurs in parallel with abnormal lipid profiles and changes in blood uric acid [18], and the activity of the erythrocyte Na+/Li+ reverse transporter (sodium-lithium countertransporter) is increased in women with left ventricular hypertrophy with insulin resistance, and patients are prone to 3, renal disorders The kidney is one of the main tissues for glucose and insulin metabolism, and hypoglycemic tolerance is closely related to renal function ...... 4, pancreatic diseases Chronic obstructive pancreatitis can lead to diabetes or hypoglycemic tolerance after destroying a large number of pancreatic endocrine cells. 5, skeletal muscle disorders Progressive myasthenia can be accompanied by DM and insulin resistance. OGTT can be used for the diagnosis and differential diagnosis of endocrine disorders and secondary DM. Many patients with endocrine disorders are accompanied by disorders of glucose metabolism (such as hyperadrenocorticism, hypoadrenocorticism, hyperthyroidism, hypothyroidism, pheochromocytoma, hypogonadism, precocious puberty, polycystic ovary syndrome, etc.), and after these corresponding diseases are cured or improved, the OGTT results will be improved accordingly. 7, acute and chronic metabolic disorders Low potassium and low magnesium can also lead to impaired insulin secretion, OGTT presents hypoglycemic tolerance.