Buffy coat

The buffy coat is the fraction of an anticoagulated blood sample that contains most of the white blood cells and platelets following density gradient centrifugation of the blood.

After centrifugation, one can distinguish a layer of clear fluid (the plasma), a layer of red fluid containing most of the red blood cells, and a thin layer in between. Making up less than 1% of the total volume of the blood sample, the buffy coat (so-called because it is usually buff in hue), contains most of the white blood cells and platelets. The buffy coat is used, for example, to extract DNA from the blood of mammals (since mammalian red blood cells are anucleate and do not contain DNA).

The buffy coat is usually whitish in color, but is sometimes green if the blood sample contains large amounts of neutrophils (which are high in green myeloperoxidase). The layer beneath the buffy coat contains granulocytes and red blood cells.

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Wikipedia