Diabetes mellitus is a metabolic disorder syndrome that can lead to multiple organ damage such as heart, brain, kidney, eye, and nerve. Therefore, when patients with suspected diabetes go to the hospital, in addition to a clear diagnosis, they should further clarify whether they have a combination of metabolic disorders such as hypertension, hyperlipidemia, obesity, and various acute and chronic complications of diabetes. Only when all these problems are clearly investigated can treatment be carried out in a better way. So, what tests should be done for diabetic patients at the initial diagnosis? Blood tests: (1) Blood glucose monitoring: Patients with diabetes should decide the frequency and time of blood glucose check according to specific conditions. In the early stage of the disease, or when adjusting the treatment plan, or changing the diet or exercise routine, it is recommended to increase the number of monitoring appropriately. (2) Liver and kidney function: Diabetic nephropathy is a common chronic complication of diabetes. Urine microalbumin quantification and renal function tests can help detect diabetic nephropathy at an early stage. Many patients with type 2 diabetes often have obesity, dyslipidemia, fatty liver and abnormal liver function, so liver function and lipid tests should also be done. (3) Lipid examination (mainly including total cholesterol, triglycerides, LDL cholesterol, etc.): diabetic patients often have dyslipidemia, which can easily cause atherosclerosis and various cardiovascular diseases. (4) Glycosylated hemoglobin measurement: reflecting the blood glucose situation 8 to 12 weeks before blood sampling, it is recommended to test once every 2 to 3 months. (5) Oral glucose tolerance test (OGTT test): When a person’s fasting blood sugar or 2-hour postprandial blood sugar is higher than normal but does not yet meet the diagnostic criteria for diabetes, an OGTT test is required to clarify whether he or she is in the impaired glucose regulation (I-GR) stage or really has diabetes. (6) Islet function measurement: It includes insulin release test (IRT) and C-peptide release test (CPRT). This test is performed by measuring the level and curve characteristics of insulin and C-peptide secretion at various points in the patient’s fasting and post-prandial periods to understand the degree of islet failure and to help determine the type of diabetes that the patient has. (7) Cellular autoantibody test: It includes the examination of glutamic acid decarboxylase antibody (GA-DA), insulin antibody (IAA) and islet cell antibody (ICA). These tests are done to identify the type of disease in diabetic patients, who tend to be positive for these antibodies in type 1 diabetes and vice versa in type 2 diabetes. The GA-DA appears early and persists for a long time in the blood of diabetic patients and is the most significant for diagnosis. Other special tests: (1) Heart and lower extremity vascular examination: For diabetic patients, the absence of heart disease symptoms does not mean that there is no heart problem, and timely electrocardiogram and cardiac ultrasound examination are necessary. Routine electrocardiogram can detect various arrhythmias and understand the blood supply to the heart muscle. In addition, lower extremity vascular ultrasound and angiography can understand the presence of lower extremity arteriosclerosis or stenosis, so that early detection of diabetic foot. (2) Blood pressure examination: The incidence of hypertension in diabetic patients is 2 to 6 times higher than that of the general population. The ideal target for blood pressure control in diabetic patients is about 120/80 mmHg. (3) Eye examination: Diabetes can cause retinopathy, and in serious cases, blindness, so fundus examination should be performed regularly and routinely. Ophthalmic examinations can detect diabetic retinopathy and cataracts, which can cause gradual loss of vision, blurred vision or sudden blindness. (4) Pulmonary CT or X-ray chest examination: The incidence of tuberculosis is 3 to 4 times higher in diabetic patients than in non-diabetic patients. Chest X-ray can clarify whether tuberculosis or lung infection is also combined. (5) Ultrasound examination of heart and abdomen: It can help to know whether diabetic patients have diabetic cardiomyopathy, cholecystitis, gallstones, kidney lesions, pancreatic calcification or stones, etc. (6) Bone densitometry: It helps to detect osteoporosis. (7) Neurological examination: Tactile examination with 10 grams of mononylon wire can detect diabetic peripheral neuropathy at an early stage. In addition, standing and lying blood pressure measurement can be done to determine whether there is “postural hypotension”; electromyography examination can understand whether there is body neuropathy. (8) Cranial CT examination: once the patient appears to have handicap, altered consciousness, distorted mouth, choking and coughing, cranial CT examination should be done to clarify whether there is cerebral hemorrhage or cerebral infarction.