血细胞比容（德语：Hämatokrit，英语：hematocrit 源于希腊语：αιματοκρίτης，简写Hct）又称血比容、红细胞压积，旧名红细胞压积（packed cell volume，简写PCV）指抗凝全血经离心后测得沉淀的血细胞(主要是红细胞)在全血中占有的比例。此数值因年龄和性别而异。正常情况下、 血细胞压积(成人)：男：40～50％，女：35～45％。根据一些医院和教科书，正常数值不同，例如：男：42～54％，女：38～46％。(另一个例子：男：36～48％，女：34～44％)

The hematocrit (/hᵻˈmætəkrᵻt/) (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells in blood. It is normally 45% for men and 40% for women. It is considered an integral part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count, and platelet count. Because the purpose of red blood cells is to transfer oxygen from the lungs to body tissues, a blood sample's hematocrit—the red blood cell volume percentage—can become a point of reference of its capability of delivering oxygen. Additionally, the measure of a subject's blood sample's hematocrit levels may expose possible diseases in the subject. Anemia refers to an abnormally low hematocrit, as opposed to polycythemia, which refers to an abnormally high hematocrit. For a condition such as anemia that goes unnoticed, one way it can be diagnosed is by measuring the hematocrit levels in the blood. Both are potentially life-threatening disorders.