Infectious diseases, electrocardiograms, blood tests and coagulation tests are usually required before colonoscopy. 1. Infectious disease examination: Since infectious diseases are usually transmitted through blood or respiratory tract, and colonoscopy is an invasive examination, infectious diseases, such as Hepatitis B, Hepatitis C, syphilis, AIDS, etc., need to be ruled out before the examination. 2. Electrocardiogram (ECG): colonoscopy is an invasive examination, which may lead to heart attack or cardiac arrest in people with heart disease, therefore, ECG is needed before the examination, and if there is any abnormality in ECG, cardiac ultrasound and 24-hour dynamic ECG may also be needed. 3. Blood routine and coagulation function tests: mainly to assess the risk of bleeding in patients. In addition, due to the new crown epidemic, a nucleic acid test is also required before colonoscopy can be performed before consultation. Consult your local medical institution for details.