Although erythrocytes are transfused to prevent or treat inadequate oxygen delivery resulting from insufficient hemoglobin concentration, specific indications for transfusion have yet to be defined. Weiskopf et al.  used nine healthy, paid volunteers to assess whether acute decrease of hemoglobin concentration to 5 g/dl would affect cerebral function.

Reaction time tests were given in sessions before the test day to familiarize patients with the procedures and to minimize postbaseline improvements in performance caused by practice effects. On the test day, using local anesthesia, two peripheral venous cannulae were inserted in each participant. Subjects used hand-held controllers to complete baseline neurobehavioral and memory tests before the removal of any blood. Tests were repeated 10–15 min after producing isovolemic anemia by removing blood into collection bags, to hemoglobin concentrations of 7, 6, and 5 g/dl. The subjects’ platelet rich plasma and 5% human serum albumen were infused intravenously at the same time that blood was withdrawn. Subjects also completed the same test procedures (including insertion of venous cannulae) given at the same time of day on separate “control study” days.

Acute reduction of hemoglobin concentration to 7 g/dl did not produce changes in reaction times or error rates, compared with data at baseline hemoglobin concentration of 14 g/dl. Subjects’ reaction time for horizontal addition and digit–symbol substitution test increased at a hemoglobin concentration of 6 g/dl, but error rate did not. At a hemoglobin concentration of 5 g/dl, immediate and delayed memory was degraded. All decrements in memory and reaction time were reversed with restoration of hemoglobin to 7 g/dl. After transfusion the next morning of all autologous erythrocytes, test results again were at baseline levels. Despite its small sample size and the fact that volunteers were not blinded to the study day, the model described here could prove useful to test the effectiveness of erythrocytes, oxygen therapeutics, or other treatments for acute anemia.