Final answer:
The hematocrit test measures the ratio of red blood cells to whole blood by spinning a blood sample in a centrifuge, separating the cellular components, and determining the volume percentage of erythrocytes.
Step-by-step explanation:
The blood test that figures the ratio of red blood cells (RBCs) to whole blood is known as the hematocrit test. This test measures the volume percentage of erythrocytes in a sample of centrifuged blood. To perform a hematocrit test, a blood sample is spun in a centrifuge, which separates the heavier erythrocytes from the lighter liquid plasma. The erythrocytes settle at the bottom of the tube, followed by a thin layer of white blood cells (WBCs) and platelets known as the buffy coat. Above this is the plasma. The hematocrit value represents the percentage of the blood sample that is composed of erythrocytes.