If a patient loses 50ml of blood during surgery, would that require a blood transfusion? how much blood loss must occur to require a blood transfusion

Absolutely not.: 50 ml of blood is a very minimal amount of blood loss in a surgery and will not result in a need for transfusion. 3 - 4 tubes of blood drawn from the arm for routine blood tests would be the equivalent. A unit of blood ranges from 250ml of packed red blood cells to 500 ml of whole blood. No need to worry. Good luck and take care.

Generally, No: However, it all depends on what the patient's hemoglobin/hematocrit was prior to surgery. If the patient was already anemic and was losing blood fast, then perhaps the anesthesiologist would order a unit of blood. Whether or not a transfusion is necessary depends on the individual's hemoglobin/hematocrit level more than how much blood is lost. Some people have a lot to spare, and others none.