Why do you need a blood test before scaling in the hospital?

Hello, because in the process of scaling the scaler will be sprayed with water to cool the operation, the water column sprayed on the head end of the scaler to produce water mist, then the patient's mouth saliva, blood will be accompanied by a large number of machine operation and sprayed out, the spattering diameter of about 1 meter, and with the air dispersal, the range of up to 5 meters, a serious contamination of the environment of the clinic and the medical equipment. In the clean treatment before it is necessary for the patient to carry out the hepatitis B virus surface antigen and HIV antibody test, to give special isolation measures for patients with infectious diseases, so as to prevent cross-infection, to protect the patient and the doctor's physical health.