The percentage of RBCs in blood is called a

The percentage of red blood cells (RBCs) in blood is commonly referred to using different terms, all of which describe the same concept. Hematocrit is the traditional term used in medical and veterinary contexts to indicate the ratio of the volume of red blood cells to the total volume of blood. This value is significant in assessing the oxygen-carrying capacity of the blood and can help diagnose various health conditions.

The abbreviation PCV stands for Packed Cell Volume, which refers to the same measurement. It is a method of quantitatively evaluating the proportion of blood made up by red blood cells after centrifugation.

Additionally, "crit" is a colloquial term often used in clinical settings to refer to the hematocrit or packed cell volume as well.

Since all these terms refer to the same measure of the proportion of red blood cells in blood, the choice indicating that all of the terms apply is accurate. Therefore, recognizing that hematocrit, PCV, and crit all describe the same measurement reinforces the understanding of blood composition in veterinary medicine.