Here are the commonly ordered lab tests by physicians today. All lab values have a normal range. They can be high, low or normal. The various cells in the blood are counted and tabulated. The count can otherwise be altered in leukemia or rare blood diseases.
White cells are part of the immune system.
Carry oxygen to the cells. Low in anemia. The stuff in the red cells that binds to oxygen. Low in anemia, by definition. A measure of total red cell volume.