Buffy coat

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Buffy coat is the fraction of a centrifuged blood sample that contains most of the white blood cells. 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, the buffy coat (so-called because it is usually buff in hue), with 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 do not contain DNA).

The buffy coat is usually whitish in color but sometimes green, if the blood sample contains large amounts of neutrophils, which are high in green myeloperoxidase.

Quantitative Buffy Coat (QBC) is a laboratory test to detect infection with malaria or other blood parasites: the blood is taken in a QBC capillary tube which is coated with acridine orange (a fluorescent dye) and centrifuged; the fluorescing parasites can then be observed under ultraviolet light at the interface between red blood cells and buffy coat. This test is more sensitive than the conventional thick smear and in >90% of cases, the species of parasite can also be identified.