Final answer:
The percentage of total blood volume composed of red blood cells is known as hematocrit. It measures the volume percentage of erythrocytes in centrifuged blood and varies normally between 36-50 percent, with normal ranges differing for males and females.
Step-by-step explanation:
The term that means the percentage of total blood volume composed of red blood cells is hematocrit. Hematocrit measures the volume percentage of erythrocytes, or red blood cells, in a sample of centrifuged blood. A hematocrit test is done by spinning a blood sample in a centrifuge, causing the erythrocytes to settle at the bottom of the test tube, given that they are the heaviest elements in blood. The resulting layer above the erythrocytes, called the buffy coat, contains the leukocytes (white blood cells) and the platelets (thrombocytes), which constitutes less than 1 percent of a blood sample. Finally, the remainder of the sample, above the buffy coat, is the plasma.
In a normal blood sample, the hematocrit levels can vary between about 36-50 percent depending on gender and other factors, with 45 percent being a typical figure. For females, hematocrit values normally range from 37 to 47, and for males, from 42 to 52. The plasma percentage thus is calculated as 100 minus the hematocrit value. Therefore, if a patient's hematocrit is 42 percent, their blood plasma would be approximately 58 percent (100 minus 42).