Final answer:
The RBC count can be measured to determine the oxygen-carrying capacity of blood.
Step-by-step explanation:
The other variable that can be measured to determine the oxygen-carrying capacity of blood is the RBC count. While hematocrit and hemoglobin concentration give information about the volume and content of red blood cells respectively, the RBC count directly measures the number of red blood cells in a given volume of blood.
By combining the measurements of hematocrit, hemoglobin concentration, and RBC count, healthcare professionals can get a comprehensive understanding of the oxygen-carrying capacity of an individual's blood.