After centrifugation, one can distinguish a layer of clear fluid (the plasma), a layer of red fluid containing erythrocytes, and a thin layer in between. Composing 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 leukocytes and thrombocytes.[2][3] 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-colored myeloperoxidase.
The buffy coat is commonly used for DNA extraction,[4] with leukocytes providing approximately 10 times more concentrated sources of nucleated cells.[5] They are extracted from the blood of mammals because mammalian erythrocytes are anucleate and do not contain DNA. A common protocol is to store buffy coat specimens for future DNA isolation and these may remain in frozen storage for many years.[6]
Diagnostic uses
Quantitative buffy coat (QBC), based on the centrifugal stratification of blood components, is a laboratory test for the detection of malarial parasites, as well as of other blood parasites.[7]
The blood is taken in a QBC capillary tube which is coated with acridine orange (a fluorescent dye) and centrifuged; the fluorescing parasitized erythrocytes get concentrated in a layer which can then be observed by fluorescence microscopy,[7] under ultraviolet radiation at the interface between erythrocytes and buffy coat. This test is more sensitive than the conventional thick smear and in over 90% of cases the species of parasite can also be identified.[8][9]
In cases of extremely low leukocyte count, it may be difficult to perform a manual differential of their various types and it may be virtually impossible to obtain an automated differential. In such cases, the medical technologist may obtain a buffy coat, from which a blood smear is made. This smear contains a much higher number of leukocytes than whole blood.[10]