In laboratories, centrifuges are used to separate fluids or liquids based on density. Centrifuges are frequently used in research and clinical laboratories to isolate cells, organelles, viruses, proteins, and nucleic acids.
How a Centrifuge Works
The term “centrifugation” refers to the application of a force that pulls spinning objects outward. It is used to separate suspended particles in a liquid based on particle size and density, rotor speed, and medium viscosity.
Gravitational force causes particles with a higher density than the solvent to sink, while particles with a lower density float to the top of a solution. Centrifugation separates particles in a solution by taking advantage of even minor differences in density.
As the rotor rotates around a central axis, a centrifugal force acts to push particles away from the axis of rotation. The particles will settle if the centrifugal force exceeds the frictional force created by the particle and buoyant forces of liquid media.
Why is Centrifugation Important in Clinical Diagnostics?
The separation of liquid and solid components in the clinical laboratory requires the use of centrifuge technology.
A serological centrifuge, for example, is routinely used in laboratories that perform biochemical analyses on body fluids to measure the volume fraction of erythrocytes in blood (the hematocrit), to separate blood cells from serum/plasma, to separate sediment from urine, and to separate bound from free components in protein binding and immunoprocedures.
The most common centrifuges used by many chemistry laboratories today are swinging bucket units and high capacity horizontal heads. These centrifuges spin the specimen tubes at a 90-degree angle to the shaft of the rotor. For 10 minutes, these machines spin the tubes at about 3500 rpm.
Coagulation and Blood Bank Centrifugation
In order to separate serum/plasma from cellular components, the clinical laboratories and blood banks rely on accurate and consistent centrifuge operation. Blood samples are spun at the blood bank for antibody screening, cell washings, and tube typing.
Differential centrifugation—a process in which the centrifugal acceleration force is adjusted to sediment certain cellular constituents while leaving others suspended—is used to separate cellular constituents within blood. During the differential centrifugation of blood, the sample is separated into two phases: a pellet made up of cellular sediment and a supernatant that can be cellular or cell-free.
A high-capacity horizontal head or swinging bucket serological centrifuge is also used in the clinical laboratories to obtain platelet-poor plasma.
Specific centrifuge parameters must be followed in order to obtain accurate analyte results in processed samples, and these parameters are specified by collection tube manufacturers. In some cases, those parameters may be analyte-specific.