 [ Symptoms ] how do doctors determine hom much blood you have lost family member bleeding internally told he only has 4 12 pints of blood left he rcvd a transfusion of 5 pints of blood [ Disease ] this was an estimation of course since the amount a blood that an adult human can be variable blood counts like a hemoglobin or hematocrit can determine to some degree the level of anemia by giving blood one unit at a time and watching the response to those tests a medical provider can estimate blood loss based on how much blood it takes to return those number to normal again just like adding oil to a car and checking the dipstick