ISSN 2398-2977      

Laboratory equipment: centrifuge

pequis

Introduction

  • A simple centrifuge is an essential piece of equipment for all in-house laboratories.

Uses

  • The centrifuge is a device that speeds up the gravitational separation of substances with differing masses. In the clinical laboratory the centrifuge is used to:
  • Remove cellular components of blood to provide a cell-free plasma or serum for analysis; 3000 rpm required; ultracentrifugation, requiring a special high speed centrifuge, may be required to consistently clear lipemic specimens.
  • Concentrate the cellular and other components of biological fluids (urine, ascites, etc) and washes (such as tracheal or bronchial   Lung: bronchoalveolar lavage  ) for microscopic/cytological examination.
  • Eliminate excessive lipid or chemically precipitated protein from an analytical sample.
  • Spin samples of anticoagulated blood to provide a rapid estimation of packed cell volume (PCV   Blood: packed cell volume (PCV)  ) and/or to assess the condition of the plasma for the presence of lipemia or jaundice.
  • Ideally blood samples for biochemical analysis should be centrifuged to separate serum/plasma from cells prior to dispatch to an external laboratory and essential before in-house analysis.

Advantages

  • Immediate separation of samples for biochemical analysis prevents or reduces sample artifacts and/or deterioration due to hemolysis during storage or transportation.

Disadvantages

  • The typical problems associated with delayed centrifugation are:
  • Artificial increase in packed cell volume (PCV) due to fluid shift into the cells, resulting in swelling of red blood cells. This also reduces plasma harvest for analysis (sometimes insufficient volume for any analysis to be carried out).
  • Leakage of constituents from cellular components into serum or plasma giving artificially high results, especially potassium as red blood cells contain high concentration of K+.
  • Increased risk of hemolysis due to red blood cell membrane breakdown/lysis.
    Hemolysis adversely affects a wide range of biochemical tests
  • Reduced glucose level due to metabolism of glucose by red blood cells.
  • When using a centrifuge it is important to balance the rotor. The weight of the tubes/racks should be equal to within 1% or the acceptable limit published by the centrifuge manufacturer.
  • Pairs of tubes/racks should be placed in the centrifuge opposite each other.
    The more accurate the balance of the rotor, the smoother the centrifuge will run, thus minimizing the disruption of cellular components
    Vibration caused by imbalance of the rotor also results in increased wear on the centrifuge and more frequent breakage of tubes
  • Care should be taken when aspirating plasma or serum from a centrifuged sample.
  • Disturbance of the cells/clot encourages the plasma/serum to become contaminated with cells giving the sample a hemolysed appearance.
  • It is also important that the cell/plasma interface is not disturbed when aspirating plasma for coagulation testing, since the plasma can become contaminated with platelets, which will interfere with accurate analysis giving falsely low clotting times.
    Careful aspiration can be achieved by aspirating the sample in stages from the top of the plasma or serum layer, rather than inserting the pipette straight to the lower portion of the plasma or serum column, which tends to cause disturbance of the cell layer

Requirements

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Further Reading

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Refereed papers

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