Which of the following is NOT a component of blood?

Hematocrit refers to the proportion of blood volume that is occupied by red blood cells, which is a measurement rather than a component of blood itself. In contrast, plasma is the liquid medium that carries blood cells, nutrients, hormones, and waste products. Leukocytes, or white blood cells, are vital for the immune response, while hemoglobin is the protein found within red blood cells that facilitates oxygen transport. Thus, while plasma, leukocytes, and hemoglobin are integral components of blood, hematocrit serves as a diagnostic measurement related to these components rather than being a constituent of blood itself.