What is measured by hematocrit?

Hematocrit specifically measures the percentage of the blood that is composed of red blood cells. This value is obtained by centrifuging a sample of blood, which separates the components based on density. The red blood cells, being the heaviest, settle at the bottom, allowing for the calculation of their proportion relative to the total blood volume.

Understanding hematocrit is crucial in various clinical settings, as it provides insight into an individual's physiological state. For instance, a low hematocrit level might indicate anemia, while a high level could suggest dehydration or other conditions such as polycythemia.

In contrast to the other options, measuring hematocrit does not directly assess oxygen levels, plasma volume, or platelet concentration. Oxygen levels are evaluated through tests such as arterial blood gas analysis, plasma volume assessment requires different techniques including measuring fluid balances or using special dyes, and platelet concentration is determined through a complete blood count (CBC). Thus, it is the measurement of the proportion of red blood cells that defines hematocrit.