What percentage of whole blood is made up of red blood cells?

The correct percentage of whole blood composed of red blood cells, typically referred to as the hematocrit, is between 38% and 48% for healthy adults. This range reflects the normal physiological conditions in which red blood cells are the most abundant cellular component of blood, playing a crucial role in the transport of oxygen from the lungs to the body's tissues and carbon dioxide from the tissues back to the lungs.

The other options such as 12-18%, 70-80%, and 50-60% do not accurately represent the typical hematocrit values. The lower range (12-18%) is more indicative of plasma component percentages or could suggest a pathological condition associated with low red blood cell counts, like anemia. The higher ranges (70-80% and 50-60%) suggest an unrealistic volume of red blood cells in circulation that would likely lead to serious health issues, such as hyperviscosity, which affects blood flow and overall circulation. Understanding these percentages helps in assessing blood health and diagnosing various conditions.