Hemoconcentration
| Hematocrit | |
|---|---|
| Medical diagnostics | |
Blood components
|
|
| MeSH | D006400 |
| MedlinePlus | 003646 |
 RBC volume
|
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.
Hematocrit is also sometimes called packed cell volume (PCV), volume of packed red cells (VPRC), or erythrocyte volume fraction (EVF). The term hematocrit comes from the Ancient Greek words haima (αἷμα, "blood") and kritēs (κριτής, "judge"). Together, hematocrit means "to separate blood". It was coined by Magnus Blix at Uppsala in 1891 as haematokrit, modeled after lactokrit, which was used in dairy farming.
With modern lab equipment, the hematocrit is calculated by an automated analyzer and not directly measured. It is determined by multiplying the red cell count by the mean cell volume. The hematocrit is slightly more accurate as the PCV includes small amounts of blood plasma trapped between the red cells. An estimated hematocrit as a percentage may be derived by tripling the hemoglobin concentration in g/dL and dropping the units.
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