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Centrifuging Blood


Serum Separator Tube

Our preference is that you use a plastic SST Vacutainer® type (serum separation tube) for most tests requiring a serum specimen. Serum separator collection tubes contain a gel that separates the clot from the serum in whole blood specimens. During centrifugation, the gel moves to create a barrier between cells and serum, providing access to the serum for various chemistry, serology and other procedures. Serum separator tubes are recommended for most testing, but please check individual specimen requirements for restrictions.


When using a serum separator tube, collect the specimen using standard venipuncture technique. Gently invert the tube five (5) times to mix the clot activator with the blood. Avoid vigorous agitation of collected specimens. Allow the tube to clot for 20-30 minutes in a vertical position. Do not centrifuge immediately after drawing the blood. Do not allow the blood to clot with the tube in a horizontal position. Do not allow the tube to stand more than one hour before centrifuging.


Centrifuge the tube for 10-15 minutes at about 1300-1800 xg. The centrifuge RPMs will differ depending on the centrifuge and rotor used. Follow the manufacturer's recommendations. The gel barrier will form, separating the serum from the clot. After centrifugation, the gel should be intact and the cells and serum completely separated. Do not re-centrifuge the tube if the barrier is incomplete. Contact the laboratory if you are having difficulty centrifuging specimens.


Many tests collected in the SST Vacutainer® (serum separation tubes) do not require transferring the supernatant serum unless the serum is to be stored frozen. Specimens transported by mail or stored more than four hours should be separated from the clot and placed into a transport tube. Polypropylene plastic test tubes are more resistant to breakage than most glass or plastic containers, especially when specimens are frozen. Legacy Laboratory Services has polypropylene transfer test tubes available for your use.


Anticoagulated Tubes (Plasma)

Plasma specimens should be collected in the designated anticoagulant tube. Gently invert the tube eight (8) times immediately after collection to evenly distribute the additive. Immediately centrifuge at 1300-1800 xg for 10-15 minutes. Carefully remove the cell-free supernatant plasma and place it in a properly labeled polypropylene test tube. Indicate that the specimen is plasma on the specimen container and test requisition. Some tests require platelet poor plasma that requires the re-centrifugation of the plasma after removal from the initial centrifugation cycle. Refer to Coagulation Specimen Collection Guidelines for more information.