Buffy coat

Blood components after centrifugation.
Human blood after separation by centrifugation. Plasma (upper layer), buffy coat (middle, white-colored layer) and erythrocyte (red blood cell) layer (bottom) can be seen.

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

Description

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. 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 white blood cells and platelets.[1][2] 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 layer beneath the buffy coat contains granulocytes and red blood cells.

The buffy coat is commonly used for DNA extraction,[3] with white blood cells providing approximately 10 times more concentrated sources of nucleated cells.[4] They are extracted from the blood of mammals because mammalian red blood cells 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.[5]

Some refer to the buffy coat when separating cells by Ficoll density gradients.[6] This usage of the expression buffy coat is incorrect.

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 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.[8][9]

In cases of extremely low white blood cell count, it may be difficult to perform a manual differential of the various types of white cells, 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 white blood cells than whole blood.[10]

See also

References

  1. ↑ Mescher, Anthony L. (2018). "Blood". Junqueira's Basic Histology: Text and Atlas (15 ed.). McGraw-Hill Education. p. 237. ISBN 9781260026184.
  2. ↑ Marieb, Elaine N. (2007). Human Anatomy & Physiology (Seventh ed.). San Francisco: Pearson Benjamin Cummings. ISBN 978-0-8053-5910-7.
  3. ↑ Mychaleckyj, Josyf C; Farber, Emily A; Chmielewski, Jessica; Artale, Jamie; Light, Laney S; Bowden, Donald W; Hou, Xuanlin; Marcovina, Santica M (10 June 2011). "Buffy coat specimens remain viable as a DNA source for highly multiplexed genome-wide genetic tests after long term storage". Journal of Translational Medicine. 9: 91. doi:10.1186/1479-5876-9-91. ISSN 1479-5876. PMC 3128059. PMID 21663644.
  4. ↑ Fabre, Anne-Lise; Luis, Aurélie; Colotte, Marthe; Tuffet, Sophie; Bonnet, Jacques (30 November 2017). "High DNA stability in white blood cells and buffy coat lysates stored at ambient temperature under anoxic and anhydrous atmosphere". PLOS ONE. 12 (11): e0188547. Bibcode:2017PLoSO..1288547F. doi:10.1371/journal.pone.0188547. PMC 5708797. PMID 29190767.
  5. ↑ Gustafson, Sarah; Proper, Jacqueline A.; Bowie, E. J. Walter; Sommer, Steve S. (1 September 1987). "Parameters affecting the yield of DNA from human blood". Analytical Biochemistry. 165 (2): 294–299. doi:10.1016/0003-2697(87)90272-7. ISSN 0003-2697. PMID 3425899.
  6. ↑ Louzao, Raul. "Buffy Coat Isolation for Manual Ficoll Methods 0001". YouTube.
  7. 1 2 Ahmed, Nishat Hussain; Samantaray, Jyotish Chandra (2014). "Quantitative Buffy Coat Analysis-An Effective Tool for Diagnosing Blood Parasites". Journal of Clinical and Diagnostic Research. 8 (4): DH01. doi:10.7860/JCDR/2014/7559.4258. ISSN 2249-782X. PMC 4064892. PMID 24959448.
  8. ↑ Sherman, Angel (2018). Medical Parasitology. EDTECH. ISBN 9781839473531.
  9. ↑ Kochareka, Manali; Sarkar, Sougat; Dasgupta, Debjani; Aigal, Umesh (October 2012). "A preliminary comparative report of quantitative buffy coat and modified quantitative buffy coat with peripheral blood smear in malaria diagnosis". Pathogens and Global Health. 106 (6): 335–339. doi:10.1179/2047773212Y.0000000024. PMC 4005131. PMID 23182137.
  10. ↑ Blumenreich, Martin S. (1990). "The White Blood Cell and Differential Count". Clinical Methods: The History, Physical, and Laboratory Examinations (3rd ed.). Butterworths. ISBN 978-0-409-90077-4. PMID 21250104.
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