How is the platelet count defined in a CBC?

In a complete blood count (CBC), the platelet count is specifically defined as the number of platelets present in a cubic millimeter (mm³) of blood. This measurement provides crucial information regarding the hemostatic function of the blood, as platelets play a vital role in blood clotting and maintaining vascular integrity. A normal platelet count is essential for proper coagulation; too few platelets can lead to bleeding disorders, while too many can increase the risk of thrombosis.

The other choices refer to different components of a CBC. For example, the count of red blood cells (RBCs) and white blood cells (WBCs) are critical for assessing the overall health and oxygen-carrying capacity of the blood, but they do not pertain specifically to platelet measurement. The percentage of blood volume occupied by hemoglobin relates to hematocrit or hemoglobin concentration, which helps evaluate anemia or other blood disorders, but it also does not provide information about the platelet count. Thus, the definition of the platelet count as the count of platelets in 1 mm³ of blood is both precise and significant for understanding the functionality of blood in various physiological and pathological conditions.