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Figure 1. Schematic of Hematocrit Determination
Blood has a liquid component (plasma) and a particulate component (blood
cells). The denser blood cells (most of which are red blood cells) will
settle in a tube, particularly if the blood is spun in a device called
a centrifuge. The fraction of the column composed of red blood cells relative
to the entire column is the hematocrit, which normally is in the range
of 40%. The upper portion is yellowish plasma. Red blood cells carry oxygen.
Blood with a low hematocrit (e.g., 20%) leaves the tissues relatively oxygen-starved
and weak. A high hematocrit (e.g., 70%) produces problems as well, but
|To determine the hematocrit, whole blood in a tube is centrifuged to
pellet the red cells (packed red cells). Plasma remains on top of the packed
red cells. The fraction of the blood that is packed red cells is the hematocrit.
In this example, the hematocrit is about 40%.
Laurence Corash, "Laboratory Hematology: Methods for the Analysis of Blood",
in Blood: Principles and Practice of Hematology, eds.
Robert I. Handin, Samuel E. Lux, Thomas P. Stossel (Philadelphia: J.B.
Lippincott Company, 1995) 23