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Hematocrit
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Hematocrit is the percentage of blood that is made up of red blood cells. It is also known as packed cell volume, because it is measured with those cells packed tightly together at the bottom of a tube.
To see it, blood is placed in a tube and centrifuged, that is, spun. It is a bit like juice with pulp that ends up separated into layers, except that here the spinning is what does the separating. The red blood cells end up at the bottom, the white blood cells and platelets in the middle, and the plasma, the liquid part, on top. Hematocrit is the height of the red layer divided by the height of the entire column. Out of every hundred parts of blood, hematocrit counts how many are red blood cells.
And it is not a fixed number. It is high at birth, it is higher in adult men than in women, and it is higher in people who live at high altitude. During pregnancy it can fall because of hemodilution, which means the blood becomes more diluted and the red layer takes up a smaller share of the column.
In brief
Hematocrit, also called packed cell volume, is the percentage of blood made up of red blood cells.
Out of every hundred parts of blood, it counts how many are red blood cells.
Centrifuged blood forms three layers: red cells at the bottom, white cells and platelets in the middle, plasma on top; the red layer's height is divided by the whole column's.
It is high at birth, higher in adult men than in women, higher in high-altitude residents, and can fall in pregnancy from hemodilution.
Sources (2)
- MedlinePlus, U.S. National Library of MedicineHematocrit Test, MedlinePlusPublished
- National Center for Biotechnology Information, StatPearls PublishingHematocrit, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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