The hematocrit or packed cell volume (PCV) or erythrocyte volume fraction (EVF) is the percentage (%) of the concentration of red blood cells in blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

. It is normally about 45% for men and 40% for women. It is considered an integral part of a person's complete blood count
Complete blood count
A complete blood count , also known as full blood count or full blood exam or blood panel, is a test panel requested by a doctor or other medical professional that gives information about the cells in a patient's blood...

 results, along with hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 concentration, white blood cell
White blood cell
White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...

 count, and platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes.  The average lifespan of a platelet is normally just 5 to 9 days...


In mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, hematocrit is independent of body size.

The term "hematocrit" comes from the German/Swedish "haematokrit" coined by Blix at Upsala in 1891 as referenced by SG Hedin in Skandanavia Arch.f Physiolgie 2:134-140,1891 in an article entitled "The Haematokrit: a New Apparatus for the Investigation of Blood." The "Haematokrit" was modeled after the "Lactokrit" which was used in dairy farming.