Blood volume is the total volume of plasma and red blood cells contained in the circulatory system. The normal value for an average adult male is 5 litres, with women having slightly less.In a healthy patient, it is regulated by the kidneys.
Blood volume can be calculated by taking a patient's hematocrit result and comparing it to the volume of plasma. It must be monitored carefully for patients with congestive heart failure, chronic high blood pressure, kidney failure, and patients in critical care situations. However, it does not appear to be a useful indicator of a patient's health when they are undergoing dialysis.